frontend: console protocol priority

this patch adds priority to ConsoleProtocol enum. This priority
determines precedence of protocols when selecting default option in the
ui.

Change-Id: I9256ef44071f40552e47f03d829d95da810086ab
Bug-Url: https://bugzilla.redhat.com/1086244
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>