[server/test] stop using email cube - make unittest_migractions use a separate datadir, and add a fake email cube there (we use it to test {add,drop}_cube, so need something that looks like a cube) - for the other test modules, just copy what we need from cubicweb-email's schema to our test schema

usr/bin/cubicweb-ctl usr/bin/
usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl