ui: add ability to specify multiple VNC listen addresses

This change allows the listen address and websocket address
options for -vnc to be repeated. This causes the VNC server
to listen on multiple addresses. e.g.

 $ $QEMU -vnc vnc=localhost:1,vnc=unix:/tmp/vnc,\
              websocket=127.0.0.1:8080,websocket=[::]:8081

results in listening on

127.0.0.1:5901, 127.0.0.1:8080, ::1:5901, :::8081 & /tmp/vnc

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170203120649.15637-9-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>