Parallel XML writers have been moved to a new module
vtkIOParalleXML (see 7355859). Tests in the ParallelMPI
module use the Parallel XML multi-block writer, hence they
now need to depend on vtkIOParallelXML, instead of
vtkIOParallel. Fixed that.

Change-Id: I5490cd9d9b5bbaeb7f1c29826f002ef97515dc4e