RBD: Improve connection debug statement
RBD: Improve connection debug statement

When the driver fails to connect to a ceph cluster, having all of the
connection parameters in the debugging statement is of great use in
diagnosing misconfiguration.

Change-Id: I5996efba202891020b859310d31c4efd45817829

openstack/cinder,j-griffith/cinder,mahak/cinder,openstack/cinder,phenoxim/cinder,phenoxim/cinder,j-griffith/cinder,mahak/cinder