No error report on update of existing config at stack deploy

[fp-pszczekutowicz]

Description
When docker stack deploy is executed and content of existing config is changed there is no error report.

Steps to reproduce the issue:

1. Create a stack

version: "3.3"
services:
  service:
    image: alpine
configs:
  my_conf:
    file: ./my.conf

and a file my.conf

CONFIG v1

2. Deploy stack: docker stack deploy -c docker-compose.yml test
3. Edit my.conf file

CONFIG v2

4. Deploy stack: docker stack deploy -c docker-compose.yml test

Describe the results you received:
No error

Describe the results you expected:
Error response from daemon: rpc error: code = 3 desc = only updates to Labels are allowed

Additional information you deem important (e.g. issue happens only occasionally):
https://github.com/docker/cli/blob/master/cli/command/stack/deploy_composefile.go

Function createConfigs does not return errors
https://github.com/docker/cli/blob/master/cli/command/stack/deploy_composefile.go#L251
https://github.com/docker/cli/blob/master/cli/command/stack/deploy_composefile.go#L257

Output of docker version:

Client:
 Version:      17.09.1-ce
 API version:  1.32
 Go version:   go1.8.3
 Git commit:   19e2cf6
 Built:        Thu Dec  7 22:24:28 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.09.1-ce
 API version:  1.32 (minimum version 1.12)
 Go version:   go1.8.3
 Git commit:   19e2cf6
 Built:        Thu Dec  7 22:23:07 2017
 OS/Arch:      linux/amd64
 Experimental: false

Output of docker info:

Containers: 8
 Running: 1
 Paused: 0
 Stopped: 7
Images: 6
Server Version: 17.09.1-ce
Storage Driver: overlay2
 Backing Filesystem: extfs
 Supports d_type: true
 Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
 Volume: local
 Network: bridge host macvlan null overlay
 Log: awslogs fluentd gcplogs gelf journald json-file logentries splunk syslog
Swarm: active
 NodeID: ycal835ulsa8e2oyb6l6y9n0c
 Is Manager: true
 ClusterID: ojac6sbck33tdgjnewl0qgmzx
 Managers: 1
 Nodes: 1
 Orchestration:
  Task History Retention Limit: 5
 Raft:
  Snapshot Interval: 10000
  Number of Old Snapshots to Retain: 0
  Heartbeat Tick: 1
  Election Tick: 3
 Dispatcher:
  Heartbeat Period: 5 seconds
 CA Configuration:
  Expiry Duration: 3 months
  Force Rotate: 0
 Autolock Managers: false
 Root Rotation In Progress: false
 Node Address: 10.57.206.96
 Manager Addresses:
  10.57.206.96:2377
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 06b9cb35161009dcb7123345749fef02f7cea8e0
runc version: 3f2f8b84a77f73d38244dd690525642a72156c64
init version: 949e6fa
Security Options:
 apparmor
 seccomp
  Profile: default
Kernel Version: 4.13.0-19-lowlatency
Operating System: Ubuntu 17.10
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 15.54GiB
Name: ************
ID: G244:BV5P:3LAX:PHPJ:DVPH:GHYC:RC2X:AZLG:JSTN:EQEI:HLVP:W7LL
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false

WARNING: No swap limit support

[thaJeztah]

Continuation of moby/moby#35108