Medium: Build: Fix the installation directory for the Shell's python modules
On openSUSE, the py_libdir rpm macro behaves more like the pyexecdir
autoconf variable (uses lib64 on 64-bit machines).
Standardize on the openSUSE definitions and change the fallback version
of py_libdir to use %{_lib} too
(transplanted from 00c6e47d32f3552b115936196757ab6091ae0f61)

Mercurial revision: 45bc82b1ee9a86c9ef10f51d8fcc8416ad8650fb