ipatests: test_replica_promotion.py: test KRA on Hidden Replica
    
    The Hidden replica tests did not test what happened when KRA was
    installed on a hidden replica and then other KRAs instantiated from
    this original one. Add a test scenario that covers this.
    
    Related: https://pagure.io/freeipa/issue/8240
    Signed-off-by: François Cami <fcami@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Michal Polovka <mpolovka@redhat.com>