cubicweb #847652 re enable testing agains real db [open]

This is precious at least when porting to a new rdbms (who said sqlserver?).

the generated skeletons need fixing and devtools probably needs some good hitting on the head.

reminder: this feature is supposed to work with:

cd mycube/test
pytest --source path/to/etc/cubicweb.d/myinstance/source realdb_test_mycube.py

with --source coming from pytestconf.py (generated by cwctl create) and realdb_test_mycube.py also generated.

prioritynormal
typeenhancement
appeared in<not specified>
done in<not specified>
load0.500
load left0.500
closed by<not specified>