Clean up unittests to work with new pep8 syntax changes

- Several unittest failing b/c of pep8 style changes
- sos/tests/plugin_tests.py:
  - Initializing a fake plugin to test was failing due to our global
    logger not being initialized. Put a simple check in the library to
    make sure the logger is defined no matter what the calling state
    does.
- Make import selinux conditional
- Add travis-ci support
- Rename README to utilize travis-ci build status
Merge branch 'hotfix/hotfix-2.3.1' into develop