Add a new argument in inet_listen()/inet_listen_opts()
to pass back listen error.

Change nbd, qemu-char, vnc to use new interface.
Signed-off-by: NAmos Kong <akong@redhat.com>
Reviewed-by: NOrit Wasserman <owasserm@redhat.com>
Reviewed-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>