'test_run_as' functional test failing when running tox with root user

'test_run_as' [1] functional test fails with below traceback when running py35 tests with root user:-
py27 test works fine, py35 works if run with non root user(this Test is skipped).

FAIL: oslo_rootwrap.tests.test_functional.RootwrapTest.test_run_as
tags: worker-2
----------------------------------------------------------------------
stdout: {{{99}}}

Traceback (most recent call last):
  File "/root/oslo.rootwrap/oslo_rootwrap/tests/test_functional.py", line 106, in test_run_as
    self.assertEqual('%s\n' % pwd.getpwnam('nobody').pw_uid, out)
  File "/root/oslo.rootwrap/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 411, in assertEqual
    self.assertThat(observed, matcher, message)
  File "/root/oslo.rootwrap/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 498, in assertThat
    raise mismatch_error
testtools.matchers._impl.MismatchError: '99\n' != b'99\n'
Ran 73 tests in 16.071s
FAILED (id=0, failures=1)
error: testr failed (1)
ERROR: InvocationError: '/root/oslo.rootwrap/.tox/py35/bin/python setup.py testr --slowest --testr-args=(?!tests.test_functional_eventlet)tests '
____________________________________________________________________ summary _____________________________________________________________________
ERROR: py35: commands failed

Reproduction step:-

Switch to root user:-
sudo su -
git clone https://github.com/openstack/oslo.rootwrap
cd oslo.rootwrap
tox -epy35

Expected Output:-
The test should pass

[1] https://github.com/openstack/oslo.rootwrap/blob/6285b63572c893391cb1a9e0c482658938f13329/oslo_rootwrap/tests/test_functional.py#L100-L110