[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>).
### Requirements for tests in various cubicweb/**/test directories. ###
## shared by several test folders
cubicweb-card
docutils
Twisted < 16.0.0
webtest
## cubicweb/test
Pygments
mock
#fyzz XXX pip install fails
cubicweb-file
cubicweb-localperms
cubicweb-tag
## cubicweb/devtools/test
flake8
## cubicweb/hooks/test
psycopg2
## cubicweb/pyramid/test
pyramid >= 1.5.0
waitress >= 0.8.9
wsgicors >= 0.3
pyramid_multiauth
## cubicweb/sobject/test
cubicweb-comment