fix Debian rule template to set default compile flags with newer dpkg-buildpackage

[dirk-thomas]

See details at ros-infrastructure/buildfarm#197

Please release a new patch version after this fix since existing packages need to be rereleased with a debinc.

[wjwwood]

Where should dpkg-buildflags be invoked? Or should we just include the buildflags.mk and where should that be done? The top of the file?

[tfoote]

I found a guideline here: https://wiki.debian.org/HardeningWalkthrough#rules_files_based_on_debhelper_and_minimised_dh.281.29 We're at compat level 7 at the moment so it looks like we need to override the dh_auto_configure