This patch allows the current ONL master branch (ref. 1537d833) to build
on Ubuntu 20.04.1. Without this patch, the following error is observed while
building using the docker/tools/onlbuilder environment when targetting
armel:
INFO:onlrfs:dpkg-configure filesystem...
DEBUG:onlrfs:Executing:sudo chroot jessie/rootfs-armel.d /tmp/configure.sh