When backup cinder or nova using freezer-agent(do not use
'path-to-backup' option), if you do not use the --mode option(Default
value 'fs' will be set), the command-line report a critial error.
So, it is better to add nova and cinder to mode cfg description.
You can also see:
https://review.openstack.org/#/c/379281/7
Change-Id: I56981278986d4a032044421e356518b814f01a78