Make installation of D-Bus configs optional
    
    Make it possible to skip installing D-Bus configuration by setting the
    installation location to "no" (or using the equivalent --without flag
    with configure).  Use this to sidestep some 'make install' errors that
    we'd hit during 'make distcheck'.
    
    Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>