ipatests: test_ipahealthcheck: print a message if a system is healthy
    
    Test if when the system is completely healthy, informative message is
    returned and not only empty output (list or json).
    
    Related: https://pagure.io/freeipa/issue/8892
    
    Signed-off-by: Michal Polovka <mpolovka@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>