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
if the return value isn ot a list then repo_list is probably not a good name