In the case that the ceph storage backing volumes is different
from the one backing ephemeral storage in nova, the auth values
in the rbd connection_info could be different and not work if
we are using the nova.conf values for ephemeral storage.
This change makes the volume connection config code for rbd
prefer the cinder connection_info values if they exist, and
only falls back to nova config values if cinder doesn't have
anything set.
Depends-On: I4655cae3212d589177d2570403b563a83aad529a
Change-Id: Idcbada705c1d38ac5fd7c600141c2de7020eae25
Closes-Bug: #1635008