storage_service: drain_on_shutdown: unregister storage_proxy subscribers from local_storage_service
storage_service: drain_on_shutdown: unregister storage_proxy subscribers from local_storage_service

Match subscription done in main() and avoid cross shard access
to _lifecycle_subscribers vector.

Fixes #5385

Signed-off-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Acked-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>
Message-Id: <20200123092817.454271-1-23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>

scylladb/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,avikivity/scylla