Jest warning on leaks if tests fail by timeout

[wawaqa]

Although this is not a critical issue, I'd suggest to have a look into it when we have time to improve the product.
If Jest tests fails by timeout, the following warning is displayed:
A worker process has failed to exit gracefully and has been force exited. This is likely caused by tests leaking due to improper teardown. Try running with --detectOpenHandles to find leaks. Active timers can also cause this, ensure that .unref() was called on them.
Steps to reproduce:

1. Set low timeout (e.g. 30 secs) in Jest
2. Run tests with scans
   

Relates to #74

[derevnjuk]

You have to align scan's timeout with jest's timeout. Otherwise, nothing prevents the async generator to execute new iterations.

[wawaqa]

maybe we should at least mention it in the documentation? of for instance pass jest timeout to the threshold if it's present by default?
The problem is also that we leave lots of scans, which either get disrupted or running forever (like the LFI one, I have scans running 2+ days old, although usually it takes minutes to finish).