udocker: switch to python3-modules and drop python-subprocess
udocker: switch to python3-modules and drop python-subprocess

Adjustments needed as we can no longer make use of python2. Switch
from using python-modules to python3-modules and use python3-core to
provide 'subprocess'.

Signed-off-by: Mark Asselstine <9d979f2c41783077c213bce515ff7ad668691d2c@windriver.com>

masselstine/meta-overc,masselstine/meta-overc,OverC/meta-overc,masselstine/meta-overc,OverC/meta-overc,OverC/meta-overc,OverC/meta-overc,masselstine/meta-overc,OverC/meta-overc,OverC/meta-overc