Add simple testing to CGNS plugin

add 5blocks_cgns test from VisIt CGNS reader
correct undefined symbols in vtkCGNSReaderInternal.cxx

Change-Id: I64c7e2ac023e31c2b64cf8612529b07471f812c9
Merge topic 'add_cgns_plugin_test' into next

8ec1f86d Add simple testing to CGNS plugin