R1:ac66522c2e27

Add a flag to ./bin/worker to select tasks based on their failureCount

Summary:
I frequently run into a situation where I want to kill tasks that have accumulated a lot of failures regardless of what class they are. Or I'll want to kill every worker of a certain class but only if it has failed at least once. This change allows me to run `./bin/worker cancel --class <MYCLASS> --min-failure-count 5` to only kill tasks with at least 5 failed attempts.

The `--min-failure-count N` argument can be used by…