gtk ui: unbreak spice

Merge of the gtk ui brought a initialitation order issue for spice:
The using_spice variable isn't set yet when checked, leading to the
default UI being activated (additionally to spice remote access).

Let's set display_remote when we find a -spice switch on the command
line, like we do for vnc.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 1361804550-15858-1-git-send-email-kraxel@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
