Fix Python3 unitests/syntax checker

[Lucas Alvares Gomes]

If you run "tox -epep8" when Python3 is your default interpreter you will get:

$ tox -epep8
...
pep8 runtests: PYTHONHASHSEED='25646210'
pep8 runtests: commands[0] | flake8
./virtualbmc/tests/unit/test_manager.py:89:33: F821 undefined name 'file'
./virtualbmc/tests/unit/test_manager.py:215:33: F821 undefined name 'file'
./virtualbmc/tests/unit/test_manager.py:237:33: F821 undefined name 'file'

Similarly, when running "tox -epy35" you will get:

virtualbmc.tests.unit.test_manager.VirtualBMCManagerTestCase.test_stop_pid_file_not_found
-----------------------------------------------------------------------------------------

Captured traceback:
~~~~~~~~~~~~~~~~~~~
    b'Traceback (most recent call last):'
    b' File "/home/lucas/Projects/virtualbmc/virtualbmc/manager.py", line 184, in stop'
    b" with open(pidfile_path, 'r') as f:"
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/mock/mock.py", line 1062, in __call__'
    b' return _mock_self._mock_call(*args, **kwargs)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/mock/mock.py", line 1118, in _mock_call'
    b' raise effect'
    b'OSError: boom'
    b''
    b'During handling of the above exception, another exception occurred:'
    b''
    b'Traceback (most recent call last):'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/mock/mock.py", line 1305, in patched'
    b' return func(*args, **keywargs)'
    b' File "/home/lucas/Projects/virtualbmc/virtualbmc/tests/unit/test_manager.py", line 242, in test_stop_pid_file_not_found'
    b' self.manager.stop, self.domain_name0)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 485, in assertRaises'
    b' self.assertThat(our_callable, matcher)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 496, in assertThat'
    b' mismatch_error = self._matchHelper(matchee, matcher, message, verbose)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 547, in _matchHelper'
    b' mismatch = matcher.match(matchee)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/matchers/_exception.py", line 108, in match'
    b' mismatch = self.exception_matcher.match(exc_info)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/matchers/_higherorder.py", line 62, in match'
    b' mismatch = matcher.match(matchee)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 475, in match'
    b' reraise(*matchee)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/_compat3x.py", line 16, in reraise'
    b' raise exc_obj.with_traceback(exc_tb)'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/matchers/_exception.py", line 101, in match'
    b' result = matchee()'
    b' File "/home/lucas/Projects/virtualbmc/.tox/py35/lib/python3.5/site-packages/testtools/testcase.py", line 1049, in __call__'
    b' return self._callable_object(*self._args, **self._kwargs)'
    b' File "/home/lucas/Projects/virtualbmc/virtualbmc/manager.py", line 189, in stop'
    b" 'found' % domain_name)"
    b' File "/home/lucas/Projects/virtualbmc/virtualbmc/exception.py", line 17, in __init__'
    b' if self.message and kwargs:'
    b"AttributeError: 'VirtualBMCError' object has no attribute 'message'"

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/virtualbmc 1.0.0 release.