Fix volume_rpcapi calls for chance/simple scheds

Change the chance and simple schedulers to pass the snapshot_id and
image_id parameters correctly volume_rpcapi, so that their values reach
cinder-volume.

Change-Id: I0abbca1fa0445c5233387a0f17363fc092d39b88
Closes-Bug: #1212710
Merge "Fix volume_rpcapi calls for chance/simple scheds"