how to roll back HDP 2.1 -> HDP 2.2 upgrade

[Brian Jeltema]

Running Ambari 2.0.2, I tried to do an upgrade to the HDP 2.2 stack. That 
upgrade
has been a disaster, and the cluster is totally screwed up. At this point I 
think my best
bet is to rollback to HDP 2.1 and try again another time. 

I didn’t see a discussion of how to do a rollback. Is this documented somewhere?
If not, can someone provide guidance?

Thanks.
Brian