cli: Allow service's networks to be updated

Resolve networks IDs on the client side.

Avoid filling in deprecated Spec.Networks field.

Sort networks in the TaskSpec for update stability.

Add an integration test for changing service networks.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

docs/reference/commandline/service_update.md

@@ -58,6 +58,8 @@ Options:
       --log-opt list                       Logging driver options (default [])
       --mount-add mount                    Add or update a mount on a service
       --mount-rm list                      Remove a mount by its target path (default [])
+      --network-add list                   Add a network
+      --network-rm list                    Remove a network
       --no-healthcheck                     Disable any container-specified HEALTHCHECK
       --placement-pref-add pref            Add a placement preference
       --placement-pref-rm pref             Remove a placement preference