Allow config of vncserver_proxyclient_address.
Allow config of vncserver_proxyclient_address.

 * Improves deployment flexibility by allowing deployers to choose which address proxies like nova-xvpvncserver should use to to connect to instance proxies.  For xenserver, this will generally be the management ip of dom0.  For libvirt, this will be the management ip of the host.
 * Fixes bug 918451
 * Renames vncserver_host to vncserver_listen for slightly better usage clarity
 * Updates docs

Change-Id: I85c9850c57ffac3dfecaec4510eb808a6a2af79c

n0ano/gantt,n0ano/gantt