CMake config: Fix CMAKE_MODULE_PATH getting erased

CMAKE_MODULE_PATH is getting cleared in client code after find_package(Paraview)

Fix it by renaming CMAKE_MODULE_PATH_save to CMAKE_MODULE_PATH_save_pv

I suspect something similar is done for VTK and that it overwrites the Paraview one.

This regression is due to !2971 (merged)

cc @ben.boeckel