[autotest] Redesign how host history is queried to avoid any DB access

The host list is retrieved from metaDB for given board and label.

BUG=chromium:419043
TEST=local run
host_history.py --board peppy -l 240
host_history.py -l 240 --hosts 172.27.213.193

Change-Id: I63595534f167b1676f62e03e0c1643479e1e1f12
Reviewed-on: https://chromium-review.googlesource.com/221743
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
5 files changed