1077506 - [RFE] Support to list details information about one specific pulp repo

https://bugzilla.redhat.com/show_bug.cgi?id=1077506
Now it is possible list information about specific repo in details, summary and specifying different fields.

This commit also contains:
- pep8
- docs
Sorry for the confusion. What I meant was that it would be clearer if this function were run without `self.command` at all. Something like:

    cudl.CreateRepositoryCommand.display_repositories(data)

This is better because one can immediately see what is being tested. IMO, `self.command` is an unnecessary abstraction. @rbarlow and I had a similar conversation about https://github.com/pulp/pulp/pull/1173