python-native: disable user site support

python-native: disable user site support

The user site-packages gets inserted into sys.path ahead of the
system site directories, so a site package installed there will
be used in preference to what's in our sysroot, causing less
deterministic builds, and potential build breakage, depending
on what the user has installed there. Disable it for our native
python, so they don't affect our builds.

(From OE-Core rev: c448bf3629ab5d930ed845d4ba48e37e4a85d2a3)

Signed-off-by: Christopher Larson <kergoth@gmail.com>
Signed-off-by: Yasir-Khan <yasir_khan@mentor.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>