db: Migrate "worker" APIs to enginefacade
db: Migrate "worker" APIs to enginefacade

Migrate worker-related APIs from the legacy enginefacade to the modern
context-based enginefacade.

Change-Id: I4a2fad1129f542665eae031eb330298687320f45
Signed-off-by: Stephen Finucane <4725dc7f3632bf126d9fbdc30c347e91e8d2fe16@redhat.com>

mahak/cinder,mahak/cinder,openstack/cinder,openstack/cinder