Docker stack rm sent to stderr

[FrenchBen]

Description

When removing a stack docker output is sent to stderr

Steps to reproduce the issue:
Given a docker-compose.yml file:

version: '3'

services:
    nginx:
        image: nginx
        deploy:
                replicas: 3

1. create a stack: docker stack deploy -c docker-compose.yml nginx
2. remove the stack and capture stdout and stderr: docker stack rm nginx 1>stdout.log 2>stderr.log

Describe the results you received:
Checking the stdout and stderr files, only the stderr had the "successful" removal calls:

Removing service nginx_nginx
Removing network nginx_default

Describe the results you expected:
I expected the remove calls to be sent to stdout. But instead they were sent to stderr.log and stdout.log is empty 😞

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

$ docker version
Client:
 Version:      17.07.0-ce
 API version:  1.31
 Go version:   go1.8.3
 Git commit:   8784753
 Built:        Tue Aug 29 17:40:27 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.07.0-ce
 API version:  1.31 (minimum version 1.12)
 Go version:   go1.8.3
 Git commit:   8784753
 Built:        Tue Aug 29 17:46:50 2017
 OS/Arch:      linux/amd64
 Experimental: true