"
Draining the database is now scattered across the do_drain()
method of the storage_service. Also it tells shutdown drain
from API drain.
This set packs this logic into the database::drain() method.
tests: unit(dev), start-stop-drain(dev)
"
* 'br-database-drain' of https://github.com/xemul/scylla:
database, storage_service: Pack database::drain() method
storage_service: Shuffle drain sequence
storage_service, database: Move flush-on-drain code
storage_service: Remove bool from do_drain
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