ProcessManager doesn't handle all processes which terminated with an error correctly

[dkarlovi]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no
Branch?	master

Currently, when a process fails with an error, process manager will claim it's still running. From the users' POV, this seems like the process "stalled", but it actually died.

There's several ways we could do this:

1. check when was the last update from the process, if it wasn't updated in some timeout, we assume it died and mark it as such, this only works for Data Definitions AFAIK
2. actually write down the PID and monitor the process' STDOUT, STDERR and if it still exists, this is much more robust, but is more complex