Support docker services from private registry on non-standard port

This MR fixes #1434 (closed)

A Docker container gitlab.example.com:4567/docker/db-fixture when included as a service is available at

• gitlab.example.com__4567__docker__db-fixture
• gitlab-example-com-4567-docker-db-fixture

Example usage

  stage: test
  services:
      - gitlab.example.com:4567/docker/db-fixture
  script:
      - export DB_CONNECT_STRING="user=test dbname=test password=test host=gitlab.example.com__4567__docker__db-fixture port=5432 sslmode=disable"
      - cd ./integration
      - make test

Disclaimer

I have no idea, what i'm doing. These are the first lines of go code, i have ever written. 🎈