Stack deploy fails if "target" or "published" port is a string

As reported by @ushuz https://github.com/docker/cli/issues/229#issuecomment-381066533

version: '3.4'
services:
    web:
        image: nginx:alpine
        ports:
          - published: '8080'
            target: 80

Deploying the above produces:

$ docker stack deploy -c docker-compose.yml hello

services.web.ports.0.published must be a integer

The same issue is present for target:

version: '3.4'
services:
    web:
        image: nginx:alpine
        ports:
          - published: 8080
            target: '80'

$ docker stack deploy -c docker-compose.yml hello 

services.web.ports.0.target must be a integer

Changing both to an integer makes this work:

version: '3.4'
services:
    web:
        image: nginx:alpine
        ports:
          - published: 8080
            target: 80

$ docker stack deploy -c docker-compose.yml hello 

Creating network hello_default
Creating service hello_web

Reproduced on:

Client:
 Version:      18.05.0-ce
 API version:  1.37
 Go version:   go1.9.5
 Git commit:   f150324
 Built:        Wed May  9 22:12:05 2018
 OS/Arch:      darwin/amd64
 Experimental: true
 Orchestrator: swarm

Server:
 Engine:
  Version:      18.05.0-ce
  API version:  1.37 (minimum version 1.12)
  Go version:   go1.10.1
  Git commit:   f150324
  Built:        Wed May  9 22:20:16 2018
  OS/Arch:      linux/amd64
  Experimental: true

Start by reproducing the quoted published and target port cases with the docker stack deploy command and trace the stack deploy port validation path. Done means both quoted numeric values are accepted like integer values, while invalid port values still fail; add or update coverage where the existing validation tests are located.