[config] retrieve last good config outside of transaction
[config] retrieve last good config outside of transaction

Call LastGoodConfig.get_by_id_async non-transactionally.

R=9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org

Bug: 742478
Change-Id: I5d003458afda8a1c4cf4cf58b7e4584a09cde491
Reviewed-on: https://chromium-review.googlesource.com/951857
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Reviewed-by: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py