Fix possible double import of cubes modules When cubes using the new layout are imported with 'cubicweb_<cube>' and with 'cubes.<cube>', the same module is imported twice. Handle this by adding 'cubes.<cube>' to sys.modules when importing from 'cubicweb_<cube>'. Move load_module() to a sub class _CubesLoader to share informations computed in find_modules(). Don't handle subpackages in _CubesImporter and rely on normal import machinery instead. Add a test and use unittest from cubicweb.devtools.testlib which resolve to unittest2 on PY2 with assertLogs() method.

[MASTER]
load-plugins=cubicweb.pylintext
ignore=__pkginfo__

[MESSAGES CONTROL]
disable = too-many-ancestors,too-many-instance-attributes,too-many-public-methods,
      too-few-public-methods,too-many-arguments,import-error

[BASIC]
function-rgx = [a-z_][a-z0-9_]{2,35}$
good-names=w,_

[TYPECHECK]
generated-members=debug,info,notice,warning,error,critical,exception

[CLASSES]
exclude-protected=_cw,_cnx,
      # namedtuple public API.
      _asdict,_fields,_replace,_source,_make


[FORMAT]
max-line-length=100
max-module-lines=2000