Log the API exception for debugging

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit f17e046319508ef9ccfe54095120cc2d4fe32c4a)
rbd: Move some logic from LibvirtComputingResource into KVMStorageProcessor

All this logic was in LibvirtComputingResource but seems redundant. Move it
into the KVMStorageProcessor
config: Only user low-case names for variables