Gergely Borsothy-Gaal

Fixed child process cleanup race condition.

1

I rather rescue the exception, since checking the status of the process would probably introduce another race condition.

Possible race condition in child process cleanup logic

1

If the SIGINT trap [here](https://github.com/aws/aws-flow-ruby/blob/master/aws-flow/lib/aws/runner.rb#L341) happens to start between [these two lines](https://github.com/aws/aws-flow-ruby/blob/master/aws-flow/lib/aws/runner.rb#L351-L352), the `workers` array possibly contains process IDs belonging to already stopped processes. This results in an `Errno::ESRCH` exception....