Fix stub_instance() to include missing attributes

The stub_instance() function aims to create a fake instance dict,
but omits several attributes present on the real database object.
This patch adds them. While they're not used anywhere (obviously)
at the moment, some WIP code I'm working on expects them to look
like the DB object, and thus fails.

Change-Id: I71fb596f8b0a80de21ee58ef378440da8eea1777
Merge "Fix stub_instance() to include missing attributes"