Add module to discover ConstraintSuites.

- Given a directory, find files matching a pattern
(e.g. "check*.py"), load these modules, and
instantiate any ConstraintSuites they define.

- Make a testdata dir with example ConstraintSuites.

BUG=chromium:1051187
TEST=python3 -m unittest discover -p *test.py

Change-Id: I68c9e57986f1c7d9ad622bc0735046c543b10ed5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/config/+/2055730
Commit-Queue: Andrew Lamb <andrewlamb@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
4 files changed