Add response schema validation for volume transfer

This is to add response schema validation for volume transfer.
Besides, created_at should be removed from the response example of
"List volume transfers for a project" in api ref,
I52a81454a995920c1ba5534fea3d50f6c9986881 will fix them.

Change-Id: If31470dac38d7f08768f43fa77bd018a932f0313
partially-implements: blueprint volume-response-schema-validation
3 files changed