[devtools/testlib] Issue a RuntimeError when a generative tests is detected Otherwise, generative tests *à la logilab-common* in CubicWebTC test cases would silently not run (at least using logilab.common.pytest runner).

usr/bin/cubicweb-ctl usr/bin/
usr/lib/python2*/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl