Add delete_snapshot and update_snapshot rules
Add delete_snapshot and update_snapshot rules

delete_snapshot and update_snapshot APIs from cinder/volume/api.py
are missing policy rules in default /etc/cinder/policy.json.
This change adds them.

Change-Id: Ie732fccd578a35e1f1f8bf1c59d5a55a2b4e928b
Closes-Bug: #1472003

scottdangelo/RemoveVolumeMangerLocks,duhzecca/cinder,sasukeh/cinder,nikesh-mahalka/cinder,dims/cinder,mahak/cinder,Datera/cinder,duhzecca/cinder,sasukeh/cinder,nikesh-mahalka/cinder,NetApp/cinder,apporc/cinder,Hybrid-Cloud/cinder,scottdangelo/RemoveVolumeMangerLocks,eharney/cinder,NetApp/cinder,mahak/cinder,Paul-Ezell/cinder-1,Datera/cinder,Paul-Ezell/cinder-1,winndows/cinder,scality/cinder,Hybrid-Cloud/cinder,ge0rgi/cinder,bswartz/cinder,eharney/cinder,scality/cinder,Nexenta/cinder,openstack/cinder,j-griffith/cinder,Nexenta/cinder,apporc/cinder,cloudbase/cinder,j-griffith/cinder,phenoxim/cinder,bswartz/cinder,dims/cinder,takeshineshiro/cinder,cloudbase/cinder,phenoxim/cinder,takeshineshiro/cinder,openstack/cinder,winndows/cinder