More build fixes for script generator plugins.

I need to make sure Python is enabled before building
the plugins and dependencies that generate the Python scripts.
I also guarded the TemporalParallelism test with PARAVIEW_DATA_ROOT.

Change-Id: Iaa0743712b025bd509a7d09b55fbade0172d3ac0
Merge topic '13048_spatio-temporal-parallelism' into next

349ddcc More build fixes for script generator plugins.