ipatests: fix expected msg in tasks.run_ssh_cmd
    
    OpenSSH 8.7p1 changed the message logged on successful
    authentication (see commit 9e1882ef6489a7dd16b6d7794af96629cae61a53).
    
    As a result, the method run_ssh_cmd is failing and needs to be
    adapted in order to be compatible with old and new openssh versions.
    
    Fixes: https://pagure.io/freeipa/issue/8989
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>