[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).
3.23 (UNRELEASED)
=================
Backwards-incompatible changes
------------------------------
* Generative tests *à la logilab-common* are not supported anymore in
`CubicWebTC`. It is advised to use the subtests_ API (available on
`CubicWebTC` either from the standard library as of Python 3.4 or through
unittest2 package otherwise).
.. _subtests: https://docs.python.org/3/library/unittest.html#distinguishing-test-iterations-using-subtests