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
@asmacdo why do you think this (cudl.ListRepositoriesCommand(self.context)).display_repositories(**data) is better then this 
self.command.display_repositories(**data) ?
In my opinion second option is more readable and quite straightforward, how do you think?