kselftests: fix RDEPENDS for python3 packages
kselftests: fix RDEPENDS for python3 packages

In newer python3 argparse and subprocess have moved into python3-core.

Signed-off-by: Anders Roxell <b4e8e89057bc64bc4f9625a4a821c9ac177a7ed2@linaro.org>

kraj/meta-96boards,mrchapp/meta-96boards,kraj/meta-96boards,96boards/meta-96boards