Variable type conversion in Compose file breaks if service name contains dot

Description

When using environment variables for integer or boolean types in a service definition, conversion will fail if the service name contains a dot (.) character.

Steps to reproduce the issue:

1. Create the following docker-compose.yml file:

version: "3"
services:
  app.0:
    image: redis
    ulimits:
      nofile:
        soft: ${APP_NOFILE}
        hard: ${APP_NOFILE}

2. Run docker stack deploy -c docker-compose.yml stk

Describe the results you received:

$ docker stack deploy -c docker-compose.yml stk
services.app.0.ulimits.nofile.hard must be a integer

Describe the results you expected:

Stack is deployed

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

Originally reported as a Compose issue: docker/compose#6279 ; realized while fixing that it applies to docker stack as well

Output of docker version:

$ docker version
Client:
 Version:           18.06.1-ce
 API version:       1.38
 Go version:        go1.10.3
 Git commit:        e68fc7a
 Built:             Tue Aug 21 17:23:18 2018
 OS/Arch:           linux/amd64
 Experimental:      false

Server:
 Engine:
  Version:          18.06.1-ce
  API version:      1.38 (minimum version 1.12)
  Go version:       go1.10.3
  Git commit:       e68fc7a
  Built:            Tue Aug 21 17:22:21 2018
  OS/Arch:          linux/amd64
  Experimental:     false

Output of docker info:

(irrelevant)

Additional environment details (AWS, VirtualBox, physical, etc.):

Reproduce the failure with the provided docker-compose.yml and the docker stack deploy -c docker-compose.yml stk command, using a dotted service name and environment-based integer values. Trace the stack deploy parsing and type-validation path to identify why the service name changes conversion, then verify that the stack deploys successfully with the same configuration.