deadlocks in nailgun tests

These tests are failed time to time:

nailgun.test.integration.test_task_managers.TestTaskManagers.test_deletion_during_deployment
nailgun.test.integration.test_charset_issues.TestCharsetIssues.test_deletion_during_deployment

Fail reason is deadlock as it's shown in logs:

test_deletion_during_deployment (nailgun.test.integration.test_task_managers.TestTaskManagers) ... Exception in thread REMOVE_NODES:
Traceback (most recent call last):
  File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
    self.run()
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/task/fake.py", line 386, in run
    handling_db_errors(resp_method, **kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/task/fake.py", line 60, in handling_db_errors
    handling_db_errors(func, retries=retries, **kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/task/fake.py", line 46, in handling_db_errors
    func(**kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/rpc/receiver.py", line 115, in remove_cluster_resp
    cls.remove_nodes_resp(**kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/rpc/receiver.py", line 55, in remove_nodes_resp
    node_db = db().query(Node).get(node['uid'])
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 775, in get
    return self._load_on_ident(key)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2512, in _load_on_ident
    return q.one()
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2184, in one
    ret = list(self)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2227, in __iter__
    return self._execute_and_instances(context)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2240, in _execute_and_instances
    close_with_result=True)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2231, in _connection_from_session
    **kw)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 777, in connection
    close_with_result=close_with_result)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 781, in _connection_for_bind
    return self.transaction._connection_for_bind(engine)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 289, in _connection_for_bind
    self._assert_is_active()
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 213, in _assert_is_active
    % self._rollback_exception
InvalidRequestError: This Session's transaction has been rolled back due to a previous exception during flush. To begin a new transaction with this Session, first issue Session.rollback(). Original exception was: (TransactionRollbackError) deadlock detected
DETAIL: Process 23546 waits for ShareLock on transaction 24210489; blocked by process 23157.
Process 23157 waits for ShareLock on transaction 24210487; blocked by process 23546.
HINT: See server log for query details.
 'DELETE FROM clusters WHERE clusters.id = %(id)s' {'id': 274}
ERROR

test_deletion_during_deployment (nailgun.test.integration.test_charset_issues.TestCharsetIssues) ... Exception in thread REMOVE_NODES:
Traceback (most recent call last):
  File "/usr/lib/python2.6/threading.py", line 532, in __bootstrap_inner
    self.run()
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/task/fake.py", line 386, in run
    handling_db_errors(resp_method, **kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/task/fake.py", line 60, in handling_db_errors
    handling_db_errors(func, retries=retries, **kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/task/fake.py", line 46, in handling_db_errors
    func(**kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/rpc/receiver.py", line 115, in remove_cluster_resp
    cls.remove_nodes_resp(**kwargs)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web/nailgun/nailgun/rpc/receiver.py", line 55, in remove_nodes_resp
    node_db = db().query(Node).get(node['uid'])
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 775, in get
    return self._load_on_ident(key)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2512, in _load_on_ident
    return q.one()
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2184, in one
    ret = list(self)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2227, in __iter__
    return self._execute_and_instances(context)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2240, in _execute_and_instances
    close_with_result=True)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/query.py", line 2231, in _connection_from_session
    **kw)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 777, in connection
    close_with_result=close_with_result)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 781, in _connection_for_bind
    return self.transaction._connection_for_bind(engine)
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 289, in _connection_for_bind
    self._assert_is_active()
  File "/home/jenkins/workspace/stackforge-verify-fuel-web_VENV/lib/python2.6/site-packages/sqlalchemy/orm/session.py", line 213, in _assert_is_active
    % self._rollback_exception
InvalidRequestError: This Session's transaction has been rolled back due to a previous exception during flush. To begin a new transaction with this Session, first issue Session.rollback(). Original exception was: (TransactionRollbackError) deadlock detected
DETAIL: Process 10497 waits for ShareLock on transaction 24280499; blocked by process 10482.
Process 10482 waits for ShareLock on transaction 24280497; blocked by process 10497.
HINT: See server log for query details.
 'DELETE FROM clusters WHERE clusters.id = %(id)s' {'id': 19}
ERROR

It's very annoying thing as tests fail in about 1/4 of CI test runs.