rgmanager: Fix corner case in critical/non-critical handling
    
    If a subtree had failed and you removed
    __independent_subtree from the configuration for that
    subtree as part of a reconfiguration operation, the
    subtree would fail to stop, causing the service to enter
    the failed state.
    
    Resolves: rhbz#634277
    
    Signed-off-by: Lon Hohberger <lhh@redhat.com>