test/py: use actual core count for parallel builds

When building U-Boot we should not blindly use make -j8 but consider the
actual core count given by os.cpu_count().

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Stephen Warren <swarren@nvidia.com>

test/py/conftest.py

@@ -156,7 +156,7 @@ def pytest_configure(config):
                 o_opt = ''
             cmds = (
                 ['make', o_opt, '-s', board_type + '_defconfig'],
-                ['make', o_opt, '-s', '-j8'],
+                ['make', o_opt, '-s', '-j{}'.format(os.cpu_count())],
             )
             name = 'make'