unittest: Allow bypassing unit tests based on private chromeos-hwid repository.

We have some unit tests maintaining HWID data integrity, but these tests should
not fail if developer only has a public source tree.

BUG=none
TEST=manual: checkout a public source tree, make test.

Change-Id: I2d26ed72a47c3fdb4758b64a81764f0ca359d0ef
Reviewed-on: https://chromium-review.googlesource.com/202891
Reviewed-by: Ricky Liang <jcliang@chromium.org>
Commit-Queue: Hung-Te Lin <hungte@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
3 files changed