[test/querier] use the new connection api (part 1/3)
In devtools/repotest, we provide a simple `.qexecute` with autocommit,
and we use it (where possible) in unittest_querier.
Note that the .session object is a real session, not the magic property
found in CubicWebTC test classes.
sync_schema_props_perms('cw_source', syncprops=False)
if schema['BigInt'].eid is None:
add_entity_type('BigInt')