Add tests for ipa-cacert-manage install
    
    Some basic tests like re-loading a certificate, loading a
    PKCS#7 cert and bad cert handling.
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    
    https://pagure.io/freeipa/issue/7579
    
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>