[test] Avoid pytest discovery warnings
Having TestServerConfiguration and alike in the test module namespace causes
pytest discovery errors, because it thinks it's a test class.
usr/lib/python2*/*-packages/cubicweb/devtools/
usr/lib/python2*/*-packages/cubicweb/skeleton/
usr/lib/python2*/*-packages/cubicweb/test
usr/lib/python2*/*-packages/cubicweb/dataimport/test
usr/lib/python2*/*-packages/cubicweb/entities/test
usr/lib/python2*/*-packages/cubicweb/ext/test
usr/lib/python2*/*-packages/cubicweb/server/test
usr/lib/python2*/*-packages/cubicweb/sobjects/test
usr/lib/python2*/*-packages/cubicweb/hooks/test
usr/lib/python2*/*-packages/cubicweb/web/test
usr/lib/python2*/*-packages/cubicweb/etwist/test