flaky TestResetBandwidthCounter test

[marten-seemann]

This is what prevents us from moving to the Unified CI setup (#189). This test is quite annoying, as it relies on time.Sleep invocations, and therefore takes 2s.

go test -run TestResetBandwidthCounter -count 100 -v ./metrics

Unfortunately, our flow metrics depend on time.Now(), there's no way to inject a clock interface, which we could mock in tests.

[Stebalien]

I'm happy to disable these tests for now. But yeah, the ability to mock time here would be even better.