[IT][Vanilla2] The check for active "nodemanager" nodes does not work

Now integration tests execute command 'sudo -u hadoop bash -lc "hadoop job -list-active-trackers"' to check how many "tasktracker" nodes are active.

This command does not work with any Vanilla2 images created with elements from sahara-image-elements repo.

Trace of tests is
======================================================================
FAIL: tests.gating.test_vanilla_two_gating.VanillaTwoGatingTest.test_vanilla_two_plugin_gating[vanilla2]
tags: worker-0
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Traceback (most recent call last):
  File "/home/skolekonov/sahara/sahara/tests/integration/tests/gating/test_vanilla_two_gating.py", line 227, in test_vanilla_two_plugin_gating
    self._create_cluster()
  File "sahara/tests/integration/tests/base.py", line 46, in wrapper
    ITestCase.print_error_log(message, e)
  File "sahara/openstack/common/excutils.py", line 68, in __exit__
    six.reraise(self.type_, self.value, self.tb)
  File "sahara/tests/integration/tests/base.py", line 43, in wrapper
    fct(*args, **kwargs)
  File "/home/skolekonov/sahara/sahara/tests/integration/tests/gating/test_vanilla_two_gating.py", line 157, in _create_cluster
    self.vanilla_two_config)
  File "sahara/tests/integration/tests/base.py", line 338, in await_active_workers_for_namenode
    % self.common_config.HDFS_INITIALIZATION_TIMEOUT
  File "/home/skolekonov/sahara/.tox/integration/local/lib/python2.7/site-packages/unittest2/case.py", line 415, in fail
    raise self.failureException(msg)
AssertionError: Tasktracker or datanode cannot be started within 5 minute(s) for namenode.

Output of command 'sudo -u hadoop bash -lc "hadoop job -list-active-trackers"' may be as follows
"Java HotSpot(TM) 64-Bit Server VM warning: You have loaded library /opt/hadoop-2.3.0/lib/native/libhadoop.so.1.0.0 which might have disabled stack guard. The VM will try to fix the stack guard now.\nIt's highly recommended that you fix the library with 'execstack -c <libfile>', or link it with '-z noexecstack'.\ntracker_sk-test-vanilla-v2-worker-node-nm-dn-002.novalocal:35697\ntracker_sk-test-vanilla-v2-worker-node-nm-001.novalocal:46901\ntracker_sk-test-vanilla-v2-worker-node-nm-dn-001.novalocal:59270\n"

A possible solution is to use the following command 'sudo -u hadoop bash -lc "hadoop job -list-active-trackers" | grep tracker_'.
Output of command 'sudo -u hadoop bash -lc "hadoop job -list-active-trackers" | grep tracker_' is
"tracker_sk-test-vanilla-v2-worker-node-nm-dn-002.novalocal:35697\ntracker_sk-test-vanilla-v2-worker-node-nm-001.novalocal:46901\ntracker_sk-test-vanilla-v2-worker-node-nm-dn-001.novalocal:59270\n"