Fetch user packages from pkdb api.

For starters the previous `PACKAGE_LIST` was not working since pkgdb2 is using new uris. Then I thought, since there is an [API](https://admin.fedoraproject.org/pkgdb/api/#user%27s_packages), why not use it?

So, `gems_owned_by(user)` now fetches a user's packages, both owned and co-maintained. If you wish to fetch only the ones a packager owns, I can simply remove the second query.

As for the tests, this method had no tests to begin with, but I'm not so familiar with rspec to test api queries. If anyone can point me how to test this, I'll happily implement it.