[tests] Don't import QUnitTestCase into tests' global namespace Unittest's test loader will try to execute QUnitTestCase's test_javascripts method. However this class is intended to be subclassed, not to be executed directly. This change has the following consequences: * slightly faster test execution * almost all rtags warnings are gone

usr/lib/python2*/*-packages/cubicweb/web
usr/lib/python2*/*-packages/cubicweb/wsgi
usr/share/cubicweb/cubes/shared/data
usr/share/cubicweb/cubes/shared/wdoc