Travis CI: a separate script to run test tasks
    
    this script is intended only for use in Travis CI and contains
    configuration of the test run requested:
    
        * it can run linter step separately by specifying TASK_TO_RUN="lint"
          environment variable in .travis.yml. In this case it also runs
          pep8 checker on the commits in PR.
        * other steps are run in developer mode in order to skip pylint run
          and speed up the task
        * in all cases the CI result log is populated and can be displayed
          if the job fails
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>