Code review comment for lp:~xnox/upstart/shrink-notifications

Backed out jodh's merged tests.
Made tests resilient to tests (pass 100+ iterations).

Fixed races:
- sigchild ariving, before read handler is called

Fixed aborts:
- due to multiple io reads, since process_fd pipe was not cleared
- job_process_error_handler returning EILSEQ
- double freeing io, when read handler is called before close handles