Fix Windows buildir pvpython config

Set pythonpath correctly when not building in VS IDE.
VTK now builds python modules in builddir/lib and
builddir/lib/site-packages. d776921c5 fixed this for
VS IDE builds.

Change-Id: I301401359a4c56edfc328cebb31b558cc0d7ec29
Merge topic 'parallel-surface-lic-pv' into next

a8686eb Fix Windows buildir pvpython config