Add note about removed cinder feature
Add note about removed cinder feature

Prior to victoria, cinder had an option to pass the content of the
keyring file as a connection property, thereby causing the situation
documented in OSSN-0085.  Add a comment in the code indicating that
this field is not passed by cinder from the victoria release onwards.

Partially-implements: bp rbd-remove-option-causing-ossn-0085
Change-Id: I4a8793753c2504f8e594f92ae7069994c2d000ad

openstack/os-brick,openstack/os-brick