cbuildbot_config: temporarily mark 'auron-paladin' not important

update-engine unit tests has been hanging on 'auron-paradin' more
frequently (chromium:678643) than other builders. This CL temporarily
marks 'auron-paladin' not important to reduce CQ failures as other
builders like 'samus-paladin' provide similar coverage. This CL will be
reverted once the issue is resolved.

BUG=chromium:678643
TEST=`./cbuildbot/cbuildbot_config_unittest`

Change-Id: Ia8bdc27dca38afc02124e962a7c5f39a95b36750
Reviewed-on: https://chromium-review.googlesource.com/427325
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
Trybot-Ready: Ben Chan <benchan@chromium.org>
2 files changed