Automatic merge from submit-queue

Add test_list command, to enumerate unit and e2e tests.

This uses go/parser and go/ast to analyze all test files in ~1 second.
It only recognizes a few simple structures that the tests all have, and
modifies a few tests to fit expected structure better.

This is part of an effort to ensure all tests have owners, by having a
verify check to catch new tests being added without an owner.