dockertest.images: Fix repo_split_p regexp

[ldoktor]

Docker looks for either '.' or ':' in order to distinguish between
repo_addr or user name, thus the name could contain other characters
and not just \w.

Signed-off-by: Lukáš Doktor ldoktor@redhat.com

[ldoktor]

This can be tested by creating image without or with weird name like "". Than when you execute some tests eg. docker_cli/pull the postprocess fails with DockerFullNameFormatError: Image name <none> do not match docker Fully Qualified Image Name format [registry_hostname[:port]/][user_name/](repository_name[:version_tag]).

This patch changes just the image name regexp, but theoretically even repo could contain non \w-matching characters. We should consider using [^:] and [^:.] everywhere. Anyway it makes sense at least for the image name.