process-manager: use better regex

A number of debug messages match /listening on/, so use a more precise
pattern.
process-manager: attach IPC channel to pm child

This allows the child to detect parent exit, and self-exit, which will
in turn cause the supervisor and any children to exit. Without this,
leaking pm child processes was possible.
Merge pull request #655 from strongloop/feature/arc-pm

arc/pm integration cleanups