Merge pull request #378 from pulp/mhrivnak-faq

adding a FAQ to the user guide that addresses checksum in unit key
adding 2.2.1 release notes
adding two more bug reports
Merge pull request #393 from pulp/mhrivnak-release-notes

adding 2.2.1 release notes
Merge pulp-2.2 => pulp-2.3, pre-build