Errata list should require either repo_id or repo info

Brad discovered that you could do `katello errata list --org=ACME
--content_view=NoSQL`. However, the errata description says that it lists
errata for a repo. Moreover, the package command that mirrors this requires
repo info. Lastly, many of the commands don't work (such as `katello errata
list --org=ACME --product_label=Mongo`) unless you specify product info. I also
talked to Garik and he confirmed that errata list is meant to list the errata
for a single repo.
Merge pull request #2079 from daviddavis/temp_1366906802

Errata list should require either repo_id or repo info