ipatests: add test for ipa-cacert-manage prune
    
    Add test for prune option of ipa-cacert-manage.
    After a certificate is installed, a jump in time
    is performed to a date where the certificate is expired,
    and then it is pruned.
    
    Related: https://pagure.io/freeipa/issue/7404
    Signed-off-by: Antonio Torres <antorres@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>