Add dpkg-buildpackage invocation to debian rules file.

This fixes #277. Which is compensating for the change in debian
packaging behavior documented in
https://github.com/ros-infrastructure/buildfarm/issues/197

We are using compat level 7 at the moment. Not sure where that's set,
but our results have compat level 7 in the debian packages. Compat
level 9 seems to deal with this automatically. Info from:
https://wiki.debian.org/HardeningWalkthrough#Enabling_dpkg-buildflags_in_your_debian.2Frules_files