add tests for paraview contour and slice plots

tests work just like cdms_verify, see wiki for how they work and
were created. I did have to add a new parameter to test infrastructure
to specify which subdirectory has regression test image.

these images were recorded on mac so we will probably need alternates for
linux were size will be slightly different
Merge remote-tracking branch 'devel/add_paraview_plot_tests'

* devel/add_paraview_plot_tests:
  add tests for paraview contour and slice plots