Refactor node-cli "integration tests"

[bkchr]

The following tests: https://github.com/paritytech/substrate/tree/master/bin/node/cli/tests often fail in CI. The problem is that they use sleep (there are other usages of sleep as well). We should remove most of these sleep calls, as they are relative bad on CI where it can happen that the system is overloaded. Instead of sleeping we should use the rpc to communicate with the node and to make sure that it produced X block for example where X is some small number like 3. This way we wait a little bit longer when the CI is overload, but we not fail with a spurious error.

Similar tests also exist in Cumulus and could use the same love afterwards.