Use ipa-docker-test-runner to run tests in Travis CI
    
    https://github.com/martbab/ipa-docker-test-runner is now used to run the
    following tasks in Travis CI:
    
    * pull in a FreeIPA test runner Docker image
    * configure/make lint/make rpms
    * install rpms
    * install FreeIPA server and KRA
    * run out-of-tree tests
    
    For performance reasons (last two steps are very time-consuming) the available
    tests were split roughly in half and are run as two separate jobs to speed up
    the process.
    
    AD trust is not installed as part of tests since the enabled compat plugin
    causes false negative errors.
    
    Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>