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.
I think it might be better if get_repositories accepted an optional argument `repo_id` and returned a list containing one dictionary. Then you could consolidate some similar code.