Ideas for speeding up test execution

[sofisl]

• [x] Make sure all previous builds are cancelled when new builds on the same PR are triggered
• [x] audit all pre & post-install scripts
• [x] perhaps copy over node modules between packages, since they're identical, vs. reinstalling? or installing centrally?
• [x] Submitting a failing check immediately if a test fails early
• [ ] Remove compileProtos step by instead doing it when running the generator and copying over to googleapis-gen
• [x] Perhaps - don't run linting on templated files, as these will always get overwritten by the post-processor