Separate endpoints for vncserver_listen and vncserver_proxyclient_address

* define new endpoint for proxy based on existing vnc endpoint
* will be used in Compute  nova-common recipe for nova.conf

Change-Id: I89298db2461b59ab8038dfc01d42f0eb69a8b58c
Partial-Bug: #1367807
Merge "Separate endpoints for vncserver_listen and vncserver_proxyclient_address"