Set test retry limit for HWTest in cbuildbot

In catastrophic cases where all the tests fail, having a lot of
retries can hurt the lab. This CL allows set a ceiling on
the number of retries that happen for HWTest.

CQ-DEPEND=CL:238421
BUG=chromium:426177
TEST=cbuildbot/run_tests

Change-Id: Iabec4e1b999376293be523ba741a5138372c9b77
Reviewed-on: https://chromium-review.googlesource.com/238590
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
Trybot-Ready: Fang Deng <fdeng@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
5 files changed