Fix typo when adding a db factory

The check on the name was done on model_factory instead of db_factory.

Author: PierreRustOrange

powerapi/cli/generator.py

@@ -182,7 +182,7 @@ def add_db_factory(self, db_name, db_factory):
         """
         add a database to generator
         """
-        if db_name in self.model_factory:
+        if db_name in self.db_factory:
             raise DatabaseNameAlreadyUsed(db_name)
         self.db_factory[db_name] = db_factory