Add a mode to burn_in_tag that will detect changes to test suites and run the entire suite on specified build variants.

As a Server Engineer,
I want changed test suites to be detected and run by burn_in_tags,
So that I can feel confident my changes work on non-required build variants.

AC:

• Changes to test suites cause the entire suite to be run on specified build variants by burn_in_tags.
• New test suites are run specified build variants by burn_in_tags.

See project scope here.