Vcs3d unstructured grid plot improvements

Fixes a hang that occurs in communication with sub-procs when plotting an unstructured grid variable in vcs3D.  Also adds some diagnostics.
>> @ThomasMaxwell<https://github.com/ThomasMaxwell> is there a listParametersValues function? It would probably be worth having so that we can explore the parameters from a script or something.

That’s' what I use printParameterValues() for.

-- Tom

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