Adding cloud-build artifacts to accelerate tests.

[cboneti]

• Dockerfile describes a container with everything needed to build and
  vet ghpc.
• hpc-tolkit-builder corresponds to the cloud-build rule to build the
  builder and then run all tests.
• hpc-toolkit-pr-validation uses the above container to validate a PR.

Submission Checklist:

• Have you installed and run this change against pre-commit? pre-commit install
• Are all tests passing? make tests
• If applicable, have you written additional unit tests to cover this
  change?
• Is unit test coverage still above 80%?
• Have you updated any application documentation such as READMEs and user
  guides?
• Have you followed the guidelines in our Contributing document?

[cboneti]

Just please notice I am explicitly skipping the go-unit-tests for the pre-commit since:

• dnephin's go-unit-tests implementation sets a hard timeout of 30s for all tests and so they timeout in cloud build.
• all the unit tests already run on the step zero of the build (make tests)

An alternative implementation, that I chose not to take was to change our .pre-commit-config.yaml to remove dnephin's go-unit-tests and add the following lines:

• repo: git://github.com/Bahjat/pre-commit-golang
  rev: c3086ee
  hooks:
  • id: go-unit-tests

I tested it and it would then work. But since the tests run in step zero, it felt preferable to reduce the runtime avoiding duplicate runs AND preventing us to take yet another dependency.

Please comment if you don't think this is a good approach.

[heyealex]

This makes sense, I like it.