[devtools] improve error message when postgresql tools are missing By default in at least Debian, some pg tools are not present in the PATH. Or they may not be installed. But the tests tools expects them to be in the PATH, and give an unhelpful 'No such file or directory' backtrace if they're not found. To help devs using the pg tests we improve the error message.

missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/share/pyshared/cubicweb/skeleton/debian/rules.tmpl)