Standardize all Docker images.

This change moves all Docker images to a standard location, and abstracts the
build process so that they can be maintained in an automated fashion. This also
allows the images to be architecture-independent.

All images will now be referred to by the test framework via the canonical
`gvisor.dev/images/<name>`, where `<name>` is a function of the path within the
source tree.

In a subsequent change, continuous integration will be added so that the images
will always be correct and available locally.

In the end, using `bazel` for Docker containers is simply not possible. Given
that we already have the need to use `make` with the base container (for
Docker), we extend this approach to get more flexibility.

This change also adds a self-documenting and powerful Makefile that is intended
to replace the collection of scripts in scripts. Canonical (self-documenting)
targets can be added here for targets that understand which images need to be
loaded and/or built.

PiperOrigin-RevId: 308322438

images/basic/python/Dockerfile

@@ -0,0 +1,2 @@
+FROM python:3
+ENTRYPOINT ["python", "-m", "http.server", "8080"]