Robot tests have been always executed in docker container, but API pyt-test is not,
so rebuild Dockerfile for it. During that, some of tools have been upgraded, so API py-test
scripts need some modification.
Signed-off-by: danfengliu <danfengl@vmware.com>
1. Add docker prune cmd to release some space;
2. Add tag for pytest in case of debugging requirement;
3. Replace image to smaller size in robot account pytest;
Signed-off-by: danfengliu <danfengl@vmware.com>
