Systemd Enabled Centos image does not work with Packer on TravisCI

[egeexyz]

Not exactly sure if this is a Centos, Packer, or TravisCI issue, but I figured I'd start here.

Summary:
Despite following the steps to enable systemd in Centos provided by the Centos image page on DockerHub, and also using the pre-enabled systemd image, the "Failed to get D-Bus connection: Operation not permitted" error message is returned.

Use Case:
I use Packer & Docker to test my Ansible roles and playbooks on TravisCI. This is the first time I've had to use Centos for them and my roles require certain Systemd units to be enabled. Needless to say, Systemd must be active for this to work.

According to this page, the only requirement besides referencing the correct image is to tell Packer to build the image in privileged mode, which I am doing:

"builders":[
    {
        "type": "docker",
        "name": "docker",
        "image": "centos/systemd",
        "privileged": "true",
        "discard": "true"
    }
]

I've also tried building the Docker image by hand, using the instructions provided by the DockerHub page. The Docker image that yielded also results in a failure.

[egeexyz]

Here's an example of running Docker in TravisCI with privileged mode on the Centos container with systemd enabled - https://travis-ci.org/egee-irl/devops_challenge/builds/365103605