Pass correct args to vol_rpc create_volume calls

In the chance and simple scheduler, create volume was originally using
snapshot_id and image_id for request_spec and filter_properties. This
corrects that by passing the correct arguments and keyword arguments to
create_volume.

Change-Id: Icbcfbfb28f36e1f75519bf5ad6fcbcc12a9b4ec1
Closes-Bug: #1212710
Merge "Pass correct args to vol_rpc create_volume calls"