[pyramid] Do not register repository.shutdown atexit in test mode It seems that there already is a special shutdown step for repository in test mode and pyramid's atexit handler interferes with it leading to assertion error about 'shutting_down' attribute being True in Repository.shutdown().

[cwconfig] don't rely on _CubeImporter while loading cubes _CubeImporter can load cube subpackages twice (there is a test for submodules in cubicweb.test.unittest_cubes.test_no_double_import() but not with a subpackage). Since _CubeImporter is for backward compatibility and is supposed to be deprecated as soon as possible, don't rely on it when loading cube schema or appobjects and always load the real modname (eg. cubicweb_<cube> if exists else cubes.<cube>).