fixes CC-177, add default timeouts to health checks

Adds default timeouts to health checks (30 seconds). Also adds support health checks to override default. Health checks are kicked off with their own process group. The group is then killed on timeout. Support for reaping zombies has also been added to the container controller. On non-zero container exit, the node controller now uses docker logs --tail=10000 to pull last 10k lines instead of reading all of the log file.
proc.ReapZombies() is a blocking call