According to the documentation for Go package time, `time.Ticker` and
`time.Timer` are uncollectable by garbage collector finalizers. They
leak until otherwise stopped. This commit ensures that all remaining
instances are stopped upon departure from their relative scopes.
Wait for specific final state instead of waiting for specific number of
operations in volume unit tests. The tests are more readable and will survive
random goroutine ordering (PV and PVC controller have both their own
goroutine).