Move hacky logic for running sky tests from mojob.py into the test list.

(Do so by running sky tests with a wrapper that always succeeds.)

I want to do this so that when I switch the recipe on the bots to using
the test list directly (instead of invoking mojob.py), we'll continue to
ignore sky test results.

R=jamesr@chromium.org

Review URL: https://codereview.chromium.org/772943002