issue #389: Use 127.0.0.1 as VNC listener IP

When setting the listener IP to 0.0.0.0 anyone can connect to the freshly
configured kimchi virtual machine manager box on port 5900, 5901, etc. and take
over any virtual machine, since VNC is per default configured by kimchi
to listen on all IPs.
As websockets proxy connects to QEMU-VNC from 127.0.0.1 also set VNC
listener IP to 127.0.0.1

Signed-off-by: Aline Manera <alinefm@linux.vnet.ibm.com>