Fix parameter description in volume and snapshot manage extension
Fix parameter description in volume and snapshot manage extension

The parameters 'cinder_id', 'reason_not_safe', 'extra_info' can be None,
but are required in the response body of listing detail of managable
volumes or snapshots.

Change-Id: Iade148d2afeaae486aab4dc789d52e9522f206ee

openstack/cinder,mahak/cinder,openstack/cinder,mahak/cinder