Improve a way to check that a network has bootstrapped

For integration tests is very useful to know programmatically when a network has bootstrapped before start using it.

I used to use a similar script to https://github.com/TheTorProject/bwscanner/blob/develop/test/scripts/install-chutney.sh#L15, which uses verify command but that stop working (don't have now the trace).

Then i realized that there was wait_for_bootstrap, but in Gitlab CI, sometimes there're relays missing, using the client and stem.

@nickm has suggested status, but it'd need more work to parse its exit.