Package python deps with dh-virtualenv

Require dh-virtualenv 0.9 package from upstream.

Build command of doom:

echo USENETWORK=yes >> /root/.pbuilderrc

DEB_BUILD_OPTIONS=nocheck git-buildpackage -nc \

--git-pbuilder \
--git-dist="precise-wikimedia" \
--git-pbuilder-options="--bindmount /packaging/deps/precise"

See debian/changelog for details.

Bug: T48552
Change-Id: I7eb60ed9ffbbb60140e1dcfd516db51732167ed0