close #472361: omit password and bytes attributes in allowed mass-mailing keys by fixing default implementation for allowed_massmail_keys() in the Emailable pluggable mixin (cw.common.mixins). Added test (in entities.test though), also fix CWUserTC classes conflicts in the test module.

#!/usr/bin/env python
from cubicweb.cwctl import run
import sys
run(sys.argv[1:])