Virtualenv invocation incompatible with virtualenv 20.0

[dspinellis]

Running dpkg-buildpackage -v -us -uc on a make-deb-generated directory on a system with virtualenv 20.0.20, results in the following fatal error message.

virtualenv: error: unrecognized arguments: --no-site-packages
Traceback (most recent call last):
[...]
/opt/venvs/epidose']' returned non-zero exit status 2
make: *** [debian/rules:4: binary] Error 1
dpkg-buildpackage: error: fakeroot debian/rules binary subprocess returned exit status 2

A workaround to avoid this problem is to amend the rules file as follows:

printf '\n\noverride_dh_virtualenv:\n\tdh_virtualenv --use-system-packages\n' >>debian/rules