Add a kolla_extend_start script to the cinder-backup service that
ensures /var/lib/cinder is owned by the 'cinder' user. See
I2d82c1ca86735d2a8d69b3e28e8cea7acd637f0b for details on what was
done for the cinder-volume service. cinder-backup also needs to run
the script because there's no guarantee the cinder-volume service
is running on every cinder-backup node.
Resolves: rhbz#2167954
Related-Bug: #1908750
Change-Id: I7fcca9fbfea87ac4b245856a3aecae9ffd211938
b6cf34a953