python3: Fix install purelib to make pip3-python work properly

python3: Fix install purelib to make pip3-python work properly

The oe-core version of python3 patches the purelib use directory to
the system libdir so as to make it work with multilibs properly inside
the patch fix_for_using_different_libdir.patch with:

-        'purelib': '{base}/lib/python{py_version_short}/site-packages',
+        'purelib': '{base}/'+sys.lib+'/python{py_version_short}/site-packages',

The problem is that this broke the pip3-python package because the
install directory is out of sync when using a multilib version of
python.  When ever a module is installed with pip3 install that is a
purelib it will get installed to a location that python3 will never
reference and cause random failures.

This patch fixes the purelib install directory to match the purelib
use directory for externally managed python modules when using
multilibs.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>