docker registry does not log in

I cannot seem to make the docker registry login work.

```
{
"MasterMachineType": "Standard_DS12_v2",
"MaxExecuteCoreCount": 100,
"DockerRegistryEmail": "xxx",
"UsePublicNetwork": true,
"ReturnProxy": true,
"DockerDescription": null,
"Credentials": "azure",
"Autoscale": true,
"MasterDockerImages": null,
"SubnetId": "xxx",
"DockerRegistryPassword": "xxx",
"UseLowPrio": true,
"Region": "australiaeast",
"DockerRegistryUsername": "xxx",
"DockerRegistryURL": "xxx.azurecr.io",
"MasterClusterInitSpecs": null,
"DefaultClusterInitSpecs": null,
"Readme": null,
"ExecuteDockerImages": null,
"ExecuteMachineType": "Standard_D32_v3",
"DockerRegistryName": "xxx",
"ImageName": "cycle.image.centos7",
"ExecuteClusterInitSpecs": null
}
```

The cluster boots, docker using dockerhub works, but trying to pull from my azure container registry does not work. I can then manually run `docker login xxx.azurecr.io -u xxx -p 'xxx'` and it works normally. In the logs I do not see the relevant lines running in the chef script:

```
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] created file /etc/systemd/system/docker.service
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] updated file contents /etc/systemd/system/docker.service
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] owner changed to 0
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] group changed to 0
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] mode changed to 644
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] sending run action to execute[systemctl daemon-reload] (immediate)
[2019-01-21T08:50:51+00:00] INFO: execute[systemctl daemon-reload] ran successfully
[2019-01-21T08:50:51+00:00] INFO: template[/etc/systemd/system/docker.service] sending run action to execute[systemctl restart docker] (immediate)
[2019-01-21T08:50:52+00:00] INFO: execute[systemctl restart docker] ran successfully
[2019-01-21T08:50:52+00:00] INFO: service[docker] enabled
[2019-01-21T08:50:54+00:00] INFO: group[add root to docker] modified
[2019-01-21T08:50:54+00:00] INFO: group[add cyclecloud to docker] modified
[2019-01-21T08:50:54+00:00] INFO: group[add dice to docker] modified
[2019-01-21T08:50:54+00:00] INFO: directory[/mnt/cluster-init] created directory /mnt/cluster-init
```

The line in https://github.com/Azure/cyclecloud-docker/blob/c81ff7f6a505cc26e695e1f17af866818f1222b0/specs/default/chef/site-cookbooks/cdocker/recipes/default.rb#L43 looks like it should log in the middle of that log.