Add volume_extensions:quotas:delete to policy.json
Add volume_extensions:quotas:delete to policy.json

Aformentioned entry was missing from default policy.json file, so the
call wasn't blocked for non-admin user. It was failing on Keystone
connection and resulted in 500 HTTP error. This addition fixes the
issue.

Closes-Bug: 1526839
Change-Id: Ib26670ea60b3e9193d91183aee35cd8aaf733068

mahak/cinder,Hybrid-Cloud/cinder,NetApp/cinder,cloudbase/cinder,dims/cinder,ge0rgi/cinder,Datera/cinder,openstack/cinder,Datera/cinder,Nexenta/cinder,Hybrid-Cloud/cinder,openstack/cinder,eharney/cinder,eharney/cinder,j-griffith/cinder,j-griffith/cinder,phenoxim/cinder,Nexenta/cinder,dims/cinder,NetApp/cinder,bswartz/cinder,cloudbase/cinder,phenoxim/cinder,bswartz/cinder,mahak/cinder