detect bad fuzzing

[fuzzah]

It would be good to detect the following situations and bail with bad exit code:

1. No fuzz stats for some time after beginning to fuzz. Note: for AFL++ there are no stats until the initial corpus was loaded, which on some binaries can take more than 30 minutes.
2. Bad coverage generated, e.g. 0% coverage.
3. Bad report generated, e.g. 0 fuzz instances, blank screenshots, 0% coverage, ...
4. Something else?

[fuzzah]

Something else:
4. Detect fuzzers being stopped by OOM-killer