Potential deadlock with multi threads & crashes in children

I ran into a small issue of using more more lines of input than the number of threads for them all with a typo to the filter such that the child threads die/exit/crash thus the .running file never get removed. This results in a deadlock situation waiting for an "available" thread below the limit given

This uses a patched up version of regressiontest to test for the cli run to exit uncleanly, in under a a certain amount of time & have a stderr error about the failure

The bio-vcf has been patched up to check for children pids via waitpid2 checks