Improve close loop

[lzap]

Handlers for splunk/cw could be improved with this:

	var result bool
	sl.closeOnce.Do(func() {
		if !sl.active.Load() {
			return
		}

		close(sl.payloads)

		for {
			select {
			case <-time.After(10 * time.Millisecond):
				if !sl.active.Load() {
					result = true
					return
				}
			case <-time.After(timeout):
				result = false
				return
			}
		}
	})

As it was suggested here: #31 (comment)