luci: Don't let the add resource button disappear after adding a VM
    
    Don't remove the "add resource" button after adding a VM to a
    service group. Previously, if you added a VM, then deleted it, you
    were not able to add more resources without refreshing the page.
    Also, it's technically legal to allow more resources, anyway, so
    luci will now allow it.
    
    Resolves: rhbz#1100831
    
    Signed-off-by: Ryan McCabe <rmccabe@redhat.com>