Avoid using the Galaxy to install/update roles

Rather than be dependent on Ansible Galaxy, this patch introduces
a custom install/update process for roles.

We don't need to worry about dependency resolution at the time being
because all of our roles are provided by DebOps.

The other benefits include:

- It is faster than Galaxy for installing
- It is much faster than Galaxy when updating (~10x improvement)
- It shows diffs when an update contains diffs
- Less chance of a network error because we avoid Galaxy's API
- More secure because it does not pass through Galaxy