Resurrect vagrant and add script to runs tests against it

Makes it easy to run the test suite against local vagrant, for the few
bugs that don't reproduce when running via fly.

[#83534066]
Improve vagrant test setup

Run tests in parallel and keep going after first suite failure.

Specify GARDEN_TEST_ROOTFS so lifecycle etc. suites run.

Beef up the README.

Ensure .gitignore includes all forms of coverage profile.

[#83534066]
Merge branch 'vagrant-up-83534066'

[#83534066]