ui: let VNC server listen on all resolved IP addresses

Remove the limitation that the VNC server can only listen on
a single resolved IP address. This uses the new DNS resolver
API to resolve a SocketAddress struct into an array of
SocketAddress structs containing raw IP addresses. The VNC
server will then attempt to listen on all resolved IP addresses.
The server must successfully listen on at least one of the
resolved IP addresses, otherwise an error will be reported.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 20170203120649.15637-7-berrange@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>