Dockertest Version 0.7.3 (No API Changes)

Signed-off-by: Chris Evich <cevich@redhat.com>
Merge pull request #119 from cevich/docker_0.7.3

Docker 0.7.3
Merge branch 'master' of https://github.com/autotest/autotest-docker into negative_test_for_docker_flag
subtest...flag: update file flag.py

Signed-off-by: Nancy <xhe@redhat.com>