Test Runner: Fixes to skipped tests. Uses a different token for skipped and not run tests in the json. The token isn't standard but should only be visible when batches report to the parent process that a test wasn't run. It shouldn't be visible to the scripts that consume test results on the bots. Also fixes the expected result for skipped tests to also be "SKIP". Bug: angleproject:5951 Change-Id: I0bd7d13b2b25b583f9c42718786cb588bacd4bc6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2894524 Reviewed-by: Yuly Novikov <ynovikov@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>