Make repolib tag matching use model.find_content

repolib now uses model.find_content to match content
required tags and product provided tags. repolib and the
ostree and container plugins now use the same code for
this.

This also removes some of the verbose debug logging that
repolib previously had.
Merge pull request #1060 from candlepin/alikins/find_content_tags

Make repolib tag matching use model.find_content