[autotest] Add an RPC to get a list of servers from server DB based on given role and status

BUG=chromium:446333
TEST=local rpc runs
DEPLOY=apache

Change-Id: I39b2c1c8c81b47b492d5eaa642ace234ff86c6a5
Reviewed-on: https://chromium-review.googlesource.com/238760
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
2 files changed