Fix wall shear stress extraction using nparts in Fieldconvert

This merge request sorts out nparts which was not working. It also introduces two tests so we can identify when it is not working next time.

The MR required some modifications into how the FieldConvertComm module executed including introducing a v_IsSerial option to identify that this is a serial communicator in reality. I have also had to put in some code into AssemblyMapCG and GenBoundaryComm (in Conditions.cpp) to ensure it realises it is a serial communicator otherwise this caused a notable delay on a large mesh when it tried to communicate bewteen many phantom partitions.

To add in regression tests I have had to modify the tester so that it can copy over a directory since the method now works by specifying a _xml:xml syntax for the xml file.

The generation of the Info.xml file when writing out a surface wall shear stress field (which is desirable) is now automatic but can also be called directly if required.