[autotest] run_suite distinguishes "not enough duts" from "board N/A"

run_suite reports INFRA_FAILURE for "not enough working duts"
run_suite reports BOARD_NOT_AVAILABLE if there is no duts at all.

BUG=chromium:376340
TEST=manually run run_suite against a pool/board without enough duts;
and a pool/board without no duts.

Change-Id: Ie0518150f117261691a5448368d4102881c37688
Reviewed-on: https://chromium-review.googlesource.com/219909
Reviewed-by: Yu-Ju Hong <yjhong@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
2 files changed