Draft: add parallel support to new EnSight readers

This adds parallel support for vtkEnSightGoldCombinedReader and vtkEnSightSOSGoldReader. These readers makes the assumption that the user will want to stick to the decomposition of parts that already exists in their casefiles. The initial strategy for this reader assigns whole casefiles to the available processes as evenly as possible. This means that using the same number of processes as number of servers listed in the SOS file is the most efficient - each rank will read one casefile. If there are more processes than casefiles, some ranks will do no work, while if there are fewer processes than casefiles, some rank(s) will read more than one casefile. Next MR will add a strategy that will consider the partition of a part in the casefile as an atomic unit, and those partitions could be more evenly distributed across ranks.