Fix memory leak in stats collector

[angelcar]

Summary

This addresses #2865 where a goroutine leak was slowly increasing memory consumption.

Implementation details

dockerGoClient.Stats creates a <-chan *types.StatsJSON which is never closed, therefore the send operation statsC <- data blocks for ever, which in turn keeps the corresponding goroutine alive for ever.

The solution is to simply do a send operation, but returning if the context (used to invoke Stats) is cancelled. This ends the offending goroutine.

i.e.

select {
case <-ctx.Done():
	return
case statsC <- data:
}

Testing

Test in a long-lived cluster and verify memory is no longer increasing indefinitely.

New tests cover the changes: yes

Description for the changelog

Bug - Fixes #2865 caused by a memory leak in stats collector.

Licensing

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.