## Problem
Our dockerfiles, for some historical reason, have unconventional names
`Dockerfile.<something>`, and some tools (like GitHub UI) fail to highlight
the syntax in them.
> Some projects may need distinct Dockerfiles for specific purposes. A
common convention is to name these `<something>.Dockerfile`
From: https://docs.docker.com/build/concepts/dockerfile/#filename
## Summary of changes
- Rename `Dockerfile.build-tools` -> `build-tools.Dockerfile`
- Rename `compute/Dockerfile.compute-node` ->
`compute/compute-node.Dockerfile`
Instead of adding them to the VM image late in the build process, when
putting together the final VM image, include them in the earlier
compute image already. That makes it more convenient to edit the
files, and to test them.
Seems nice to keep all these together. This also provides a nice place
for a README file to describe the compute image build process. For
now, it briefly describes the contents of the directory, but can be
expanded.
