This patch adds jsonschema validation for below group snapshots API's
* POST /v3/{project_id}/group_snapshots
* POST /v3/{project_id}/group_snapshots/{group_snapshot_id}/action
Made changes to unit tests to pass body as keyword argument as wsgi
calls action method [1] and passes body as keyword argument.
[1] https://github.com/openstack/cinder/blob/master/cinder/api/openstack/wsgi.py#L997
Change-Id: Ie3b8ffb209b30edf2a26a935aab840441b43adfa
Partial-Implements: bp json-schema-validation