More canonical test.
There is an exception happening around here in some cases when connection is dropped while waiting for answer. Not sure that this fixes it but this is anyhow better.

PLCObject got more methods serialized through worker : Start, Stop, NewPLC.
This particularly helps with initialization/startup/re-load problems
when targeting Xenomai. It should help in general for runtime robustness,
since those operations aren't meant to be executed concurrently.