docker service rollback: fix non-zero exit code in some cases

Before this change:
--------------------------------------------

    $ docker service create --replicas=1 --name foo -p 8080:80 nginx:alpine
    t33qvykv8y0zbz266rxynsbo3
    overall progress: 1 out of 1 tasks
    1/1: running   [==================================================>]
    verify: Service converged

    $ echo $?
    0

    $ docker service update --replicas=5 foo
    foo
    overall progress: 5 out of 5 tasks
    1/5: running   [==================================================>]
    2/5: running   [==================================================>]
    3/5: running   [==================================================>]
    4/5: running   [==================================================>]
    5/5: running   [==================================================>]
    verify: Service converged

    $ echo $?
    0

    $ docker service rollback foo
    foo
    rollback: manually requested rollback
    overall progress: rolling back update: 1 out of 1 tasks
    1/1: running   [>                                                  ]
    verify: Service converged

    $ echo $?
    0

    $ docker service rollback foo
    foo
    service rolled back: rollback completed

    $ echo $?
    1

After this change:
--------------------------------------------

    $ docker service create --replicas=1 --name foo -p 8080:80 nginx:alpine
    t33qvykv8y0zbz266rxynsbo3
    overall progress: 1 out of 1 tasks
    1/1: running   [==================================================>]
    verify: Service converged

    $ echo $?
    0

    $ docker service update --replicas=5 foo
    foo
    overall progress: 5 out of 5 tasks
    1/5: running   [==================================================>]
    2/5: running   [==================================================>]
    3/5: running   [==================================================>]
    4/5: running   [==================================================>]
    5/5: running   [==================================================>]
    verify: Waiting 1 seconds to verify that tasks are stable...

    $ echo $?
    0

    $ docker service rollback foo
    foo
    rollback: manually requested rollback
    overall progress: rolling back update: 1 out of 1 tasks
    1/1: running   [>                                                  ]
    verify: Service converged

    $ echo $?
    0

    $ docker service rollback foo
    foo
    service rolled back: rollback completed

    $ echo $?
    0

    $ docker service ps foo
    ID             NAME      IMAGE          NODE             DESIRED STATE   CURRENT STATE           ERROR     PORTS
    4dt4ms4c5qfb   foo.1     nginx:alpine   docker-desktop   Running         Running 2 minutes ago

Remaining issues with reconciliation
--------------------------------------------

Note that both before, and after this change, the command sometimes terminates
early, and does not wait for the service to reconcile; this is most apparent
when rolling back is scaling up (so more tasks are deployed);

    $ docker service rollback foo
    foo
    service rolled back: rollback completed

    $ docker service rollback foo
    foo
    rollback: manually requested rollback
    overall progress: rolling back update: 1 out of 5 tasks
    1/5: pending   [=================================>                 ]
    2/5: running   [>                                                  ]
    3/5: pending   [=================================>                 ]
    4/5: pending   [=================================>                 ]
    5/5: pending   [=================================>                 ]
    service rolled back: rollback completed

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/service/progress/progress.go

@@ -140,7 +140,8 @@ func ServiceProgress(ctx context.Context, client client.APIClient, serviceID str
 				return fmt.Errorf("service rollback paused: %s", service.UpdateStatus.Message)
 			case swarm.UpdateStateRollbackCompleted:
 				if !converged {
-					return fmt.Errorf("service rolled back: %s", service.UpdateStatus.Message)
+					progress.Messagef(progressOut, "", "service rolled back: %s", service.UpdateStatus.Message)
+					return nil
 				}
 			}
 		}