ipa-cacert-manage: add prune option
    
    Add prune option to ipa-cacert-manage, allowing
    to remove all expired certificates from the certificate store.
    
    Related: https://pagure.io/freeipa/issue/7404
    Signed-off-by: Antonio Torres <antorres@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>