tell vtk what python modules to install and where

Change-Id: I6d00b0a9b66dda763b6a4b20f6f64d144c2b6c79
Make sure VTK Python modules get build into $BUILD/lib/site-packages/*

Change-Id: Ica6be14a38873c9566d5ec679857ee18544016ee
Merge topic 'fix-python-cmake-rules' into next

25c073c Make sure VTK Python modules get build into $BUILD/lib/site-packages/*
252e549 tell vtk what python modules to install and where