[autotest] Add freon support to balance_pool.

This adds support for balancing DUTs bewteen freon and non-freon
board pools.

BUG=chromium:492264
TEST=manual tests using -n

Change-Id: Id824937314a3477e76107967a76bdfcde666fd49
Reviewed-on: https://chromium-review.googlesource.com/273329
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
1 file changed