Make pep8 related fixes to bridge_reachability test.
Pep8 related improvements to dns consistency test.
Pylint and pyflakes improvements to all stable tests.
Merge branch 'improve/pep8'

* improve/pep8:
  Pylint and pyflakes improvements to all stable tests.
  Pep8 related improvements to dns consistency test.
  Make pep8 related fixes to bridge_reachability test.