Only call add_agent_to_security_domain_admins() when CA is installed
    
    This allows the RA agent to manage the pki security domain and is
    only needed if a CA has been configured. Only call it in a CA-ful
    installation.
    
    https://pagure.io/freeipa/issue/8956
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Francois Cami <fcami@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>