make some tests run faster by removing time.Sleeps and modifying implementation

[brenol]

Hello!

I made some modifications to pipe_test.go so we use channels to signal we have closed/we are not ready anymore (timing out).

I hope this is a correct implementation as some tests are flaky (i.e. even with incorrect changes they seemed to be passing).

Thanks!

[msftclas]

All CLA requirements met.