Minor refactoring to make TestingUtilities.waitStopListening() consistent with the JavaDocs

[trgpa]

As mentioned in #3549, TestingUtilities.waitStopListening(serverConnectionFactory, delayArg) actually waits for delayArg * 2 milliseconds which is inconsistent with the JavaDocs. I think we should revise this method and increase delayArg when calling it.
For instance TestingUtilities.waitStopListening(server1, 10000L) to TestingUtilities.waitStopListening(server1, 20000L)

[artembilan]

I think we need to change that if (n++ > 200) { to the if (n++ > 100) { as it was before.
We can change the consumer of this API as you suggest for 20 seconds eventually if we really face a timing problem.
This way we are going to be consistent with API and JavaDocs for them.