Fix typo with vncserver_listen and internal_address

If vncserver_listen is not set, it should properly fall back to
internal_address_real.

This fixes an issue with libvirt trying to resolve 'False' as a
hostname:

   getaddrinfo(False,5900): Name or service not known

Change-Id: I072aceb4e61c8714b3b0d272c19d10e295fc2eae
Signed-off-by: Paul Belanger <paul.belanger@polybeacon.com>