This is the CLI change required to support non-disruptive backup
for volumes in 'in-use' status. A force flag is added to the create
backup CLI. The force flag needs to be True when backing up an
'in-use' volume. By default it is False and it is not needed when
backing up an 'available' volume.
The Cinder server side change is merged:
https://review.openstack.org/#/c/193937/
Partial-implements blueprint non-disruptive-backup
Change-Id: I53aff3973cc6365a5b1d40c21b0885c1d8166df5
2c3169e55e