Add zsh completion for 'docker service {create,update} --container-label{-add,-rm}'

Signed-off-by: Steve Durrheimer <s.durrheimer@gmail.com>

contrib/completion/zsh/_docker

@@ -1106,6 +1106,7 @@ __docker_service_subcommand() {
             _arguments $(__docker_arguments) \
                 $opts_help \
                 $opts_create_update \
+                "($help)*--container-label=[Container labels]:label: " \
                 "($help)--mode=[Service Mode]:mode:(global replicated)" \
                 "($help -): :__docker_images" \
                 "($help -):command: _command_names -e" \
@@ -1166,6 +1167,8 @@ __docker_service_subcommand() {
                 $opts_help \
                 $opts_create_update \
                 "($help)--arg=[Service command args]:arguments: _normal" \
+                "($help)*--container-label-add=[Add or update container labels]:label: " \
+                "($help)*--container-label-rm=[Remove a container label by its key]:label: " \
                 "($help)--image=[Service image tag]:image:__docker_repositories" \
                 "($help -)1:service:__docker_complete_services" && ret=0
             ;;