Mark backup_swift_key option as secret
Mark backup_swift_key option as secret

The backup_swift_key StrOpt needs to be marked secret to avoid it
from getting printed in the cinder log.

Change-Id: I6466aec5fa9001619c310bfb550851b13cc9719b
Closes-Bug: #1633623

ge0rgi/cinder,openstack/cinder,Hybrid-Cloud/cinder,mahak/cinder,phenoxim/cinder,j-griffith/cinder,j-griffith/cinder,eharney/cinder,Datera/cinder,phenoxim/cinder,Datera/cinder,mahak/cinder,Hybrid-Cloud/cinder,openstack/cinder,eharney/cinder