Possible goroutine leak in Swarm.Start

[janos]

A goroutine created in Swarm.periodicallyUpdateGauges method is not terminated when Swarm.Stop is called. After a new call to Swarm.Start, another goroutine will be created with the same functionality.

This is a nonissue for production, since the Swarm is started only once. This only affects tests where Swarm is used as a service in simulations and if stop is called too many times.

Should we add more complexity or leave it as it is?