Added CellMask support to the MPAS reader.

MPAS reader can now read cell masks to blank out land cells.
Use Threshold to remove cells that have a CellMask of 0.
Note that the variable is actually called vertexMask in the
file. This is because we are loading the dual (triangle) grid
where vertex (primary grid) == cell (dual grid).

Change-Id: Ia6171b932de338fac8f0622f2c8dc84ab4f592c6
Fix interactive paraview sessions on cross compiled crays.

If we run into systems again that lack sockets, we can revisit
this check and do it well.

Change-Id: Ifb1efe7f054cf7b677bf2a5095785919119874d5
Merge topic 'mpas-cell-mask' into master

21ab9189 Added CellMask support to the MPAS reader.
Merge topic 'fix-cray-interactive-paraview' into master

7d2f9e62 Fix interactive paraview sessions on cross compiled crays.