add rabbit_virtual_host passthrough to cinder

Change-Id: Idf296fc5e45ad08a070c4e3bc5c2f0dae38ffbba
Add vncproxy_host option

  - vncproxy host variable wa assumed to be acceptable as public_address.
    However this arg is also used for API end points in keystone.
    In order to use different endpoint address and vncproxy listen address this arg needs to be an option.

Change-Id: I0b5278c7867f384581e93d71ae158f58529a6c10