IOC Test Framework: Multithreaded IOC testing

[LiamPanchaud]

As a developer, I would like the IOC Testing framework to be able to boot IOCs in parallel for concurrent testing.

This would vastly speed up testing and Jenkins builds. It would allow us to test for errors caused by changes to the framework much faster, and potentially before Jenkins tried to build it, which would help us keep our builds green.

[Tom-Willemsen]

Some progress on branch Ticket3595_multithreaded_ioc_tests.

Work still to be done:

• Figure out the cause of the crash leading to interpreter exit code -1073741819 (only happens occasionally when running all tests)
• Reduce the amount of message interleaving fro the various threads. Probably need to introduce a proper log framework rather than ad-hoc print statements for this.
• Verify that the tests actually run ok in parallel