[autotest] Check if it's running in chroot when determining if the system is moblab

BUG=chromium:454583
TEST=test_that, confirm no error message:
"Unable to determine if this is a moblab system"

Change-Id: I3ae7e0ad47bc00f2098dde4342384dbdc7aa5dbe
Reviewed-on: https://chromium-review.googlesource.com/247408
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Simran Basi <sbasi@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
1 file changed