The start/stop sequence we're moving towards assumes a shutdown (or
drain) method that will be called early on stop to notify the service
that the system is going down so it could prepare.
For gossiper it already means calling stop_gossiping() on the shard-0
instance. So by and large this patch renames a few stop_gossiping()
calls into .shutdown() ones.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>
e24c5034b5