Docker module choose random port if we didn't pass ports variable.

[Khoa Nguyen]

In 1.8.0 version, If I didn't pass "ports" variable, Docker module will not bind any port to the Docker Host. It worked correctly.

However, In 1.9.0.1, Docker module choose a random ports, and bind to Docker Host. I think there is something wrong. Please correct me if I wrong. 

If I remove this line (  ports: "{{ docker_ports|default(omit) }}" ) , the docker module works correctly.

```

  - name: Run docker container

     docker:

       image: "{{ docker_image }}"

       name: "{{ docker_name }}"

       command: "{{ docker_command|default(omit) }}"

       ports: "{{ docker_ports|default(omit) }}"

       env: "{{ docker_env|default(omit) }}"

       volumes: "{{ docker_volumes|default(omit) }}"

```