[autotest] Puppy lab testing environment.

This is the first commit for a more reliable testing
environment for ChromeOS lab infrastructure. It creates
a class capable of mocking out job results without
turning the parsing operation into a no-op. This allows
us to schedule tests against fake DUTs without actually
needing to ssh-into them, which is pretty much all that
dummy_Pass actually does.

The cl also sneaks in a fix to hide the exception stack trace
from run_pylint.

TEST=Ran bvt.
BUG=chromium:423225,chromium:425347

Change-Id: I5ecbcf1ff08bf9f45af26333c2ccb4c4022a97d6
Reviewed-on: https://chromium-review.googlesource.com/227783
Reviewed-by: Prashanth B <beeps@chromium.org>
Commit-Queue: Prashanth B <beeps@chromium.org>
Tested-by: Prashanth B <beeps@chromium.org>
6 files changed