Prior to this change, the "name" field in
the response for "Update a snapshot's metadata"
referred to volume transfers instead of snapshots.
Make "name" a generic parameter in case it is reused
in other APIs, and make specific parameters for
snapshots and transfers.
(Similar to I0b0a692139)
Change-Id: Ifb93bd1b20c216fd29ea90c4ac70709bee569d1d
70912ef15e