Update for cliff commandmanager >=1.6.1

Cliff 1.6.1 added  CommandManager.load_commands() so we can adopt it
rather than rolling our own.

Also, that second group is Greek, not Latin.  Jeez...

Change-Id: I4a63c22f37bcfd0ef5d83c2dbd08b58fda0db35c
Merge "Update for cliff commandmanager >=1.6.1"