subtests.docker_cli.build: Add two new subtests

This pull request fixes issue https://github.com/autotest/autotest-docker/issues/230. For now I used path to my special git repo hosted on github. It could stay like that or we can create this repo within the autotest namespace. The only requirement for this repo is that the docker files are stored in root.

These subtests use https and git repository as source path for
docker build.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
These URL's are going to vary so frequently depending on where/how the test is running.  I think it's probably better to put them in as comments and have the test toss a ``DockerTestNAError`` if not provided.  This is the behavior we follow in other tests that rely on external content.  Assuming this is the only problem, I'll just fix it before merging.