python3-native: Disable pip on native builds to fix Autobuilder issues

python3-native: Disable pip on native builds to fix Autobuilder issues

As Python-3.4 pip is required and installed by default, pips installation
is bootstrapped using python wheels, this makes it complicated to patch
and causes errors on the Autobuilders, since we don't need pip for
python3-native, this disables it fixing the issues.

(From OE-Core rev: f279f1df6429b0f76e5354c6f0f0b5c29f558edd)

Signed-off-by: Alejandro Hernandez <alejandro.hernandez@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>