Testing images for slurm, pbs, are no longer buildable

When trying to rebuild the docker images used to test pbs/slurm/hadoop, the base image can't rebuild because of...

```
=> ERROR [3/7] RUN yum install -y sudo git && yum clean all && rm -rf /var/cache/yum 0.5s
------
> [3/7] RUN yum install -y sudo git && yum clean all && rm -rf /var/cache/yum:
0.271 Loaded plugins: fastestmirror, ovl
0.430 Determining fastest mirrors
0.459 Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=container error was
0.459 14: curl#6 - "Could not resolve host: mirrorlist.centos.org; Unknown error"
```

If we can migrate to debian or ubuntu for example, that would be great - but this image is the base image for three kinds of situations (slurm, openpbs, hadoop), so it can be tricky to do this.