Update snapshot rest api to be consistent with volumes

display_name becomes name and display_description becomes description in
both parameters to pass in requests and keys returned from responses.
This does not update the snapshot model as it takes the same approach
with updating the volume rest api.

Change-Id: I413b5f87882a216b7a847fb12c31f5e5ed91510b
Merge "Update snapshot rest api to be consistent with volumes"