Add test for private docker images
Add test for private docker images

Signed-off-by: Hristo Iliev <de8b97f2ffa4e66d2537fdeefa6c844accc4481a@gmail.com>

cloudfoundry-incubator/docker-cache-acceptance-tests,cloudfoundry-incubator/docker-cache-acceptance-tests,cloudfoundry-incubator/docker-registry-acceptance-tests,cloudfoundry-incubator/docker-registry-acceptance-tests