network: Add another collision check into networkCheckRouteCollision
    
    The comment above that function says: "This function can be a lot more
    exhaustive, ...", so let's be.
    
    Check for collisions between routes in the system and static routes
    being added explicitly from the <route/> element of the network XML.
    
    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1094205
    
    Signed-off-by: Martin Kletzander <mkletzan@redhat.com>