Update existing tests to actually use >1 thread and introduce new tests on the compatability of single-threaded vs 8.

The existing tests weren't actually running with multiple threads, due to the use of the pickled configuration.

Also added new tests which try to compare the ESD output. They should crash before this stage at the moment, but one day they might succeed!

Currently the Muon algorithms are not clonable (which is correct, since they are not MT compliant) but we need to make them so for testing. So I've added some configuration to override this.