Brings a set of machines down.
Returns 200 OK when the operation was successful.
Returns 307 TEMPORARY_REDIRECT redirect to the leading master when current master is not the leader.
Returns 503 SERVICE_UNAVAILABLE if the leading master cannot be found.
POST: Validates the request body as JSON and transitions the list of machines into DOWN mode. Currently, only machines in DRAINING mode are allowed to be brought down.
This endpoint requires authentication iff HTTP authentication is enabled.