BUG #15085: Fix install rules for vtkPVPythonCatalystPython.

The Python files for the separately built vtkPVPythonCatalystPython were
not getting installed. Fixed that.

Change-Id: I898b78b2b4d7a448adefcae0e56cbd3d3d50d8f0
Merge topic '15085_fix_install_rules_for_catalyst' into next

c39975a3 BUG #15085: Fix install rules for vtkPVPythonCatalystPython.