Bug 1370515

Description of problem:
The test suite is relying on flake8 installed outside the rpm packaging.
flake8 is now assuming to use python3 and fails to build:

00:01:33.469   Running setup.py install for pbr
00:01:33.469     Traceback (most recent call last):
00:01:33.470       File "<string>", line 1, in <module>
00:01:33.470       File "/home/jenkins/workspace/repoman_master_check-patch-el7-x86_64/repoman/.tox/pep8/build/pbr/setup.py", line 22, in <module>
00:01:33.470         **util.cfg_to_args())
00:01:33.470       File "pbr/util.py", line 264, in cfg_to_args
00:01:33.470         wrap_commands(kwargs)
00:01:33.470       File "pbr/util.py", line 573, in wrap_commands
00:01:33.470         cmdclass = ep.load(False)
00:01:33.470       File "/home/jenkins/workspace/repoman_master_check-patch-el7-x86_64/repoman/.tox/pep8/lib/python2.7/site-packages/pkg_resources.py", line 2260, in load
00:01:33.470         entry = __import__(self.module_name, globals(),globals(), ['__name__'])
00:01:33.471       File "/home/jenkins/workspace/repoman_master_check-patch-el7-x86_64/repoman/.tox/pep8/lib/python2.7/site-packages/flake8/main/setuptools_command.py", line 6, in <module>
00:01:33.471         from flake8.main import application as app
00:01:33.471       File "/home/jenkins/workspace/repoman_master_check-patch-el7-x86_64/repoman/.tox/pep8/lib/python2.7/site-packages/flake8/main/application.py", line 12, in <module>
00:01:33.471         from flake8 import style_guide
00:01:33.471       File "/home/jenkins/workspace/repoman_master_check-patch-el7-x86_64/repoman/.tox/pep8/lib/python2.7/site-packages/flake8/style_guide.py", line 3, in <module>
00:01:33.471         import enum
00:01:33.471     ImportError: No module named enum
00:01:33.472     Complete output from command /home/jenkins/workspace/repoman_master_check-patch-el7-x86_64/repoman/.tox/pep8/bin/python2.7 -c "import 


Please avoid to use packages not installable via yum / dnf;