Currently, sqlalchemy.ModelBase.__contains__() catches any exception,
and by doing that, it hides real bugs. For example, a Nova unit test
raises the following error, but __contains__() simply returns False:
sqlalchemy.orm.exc.DetachedInstanceError: Parent instance
<InstanceExtra at 0x7fea635bc5f8> is not bound to a Session;
deferred load operation of attribute 'pci_requests' cannot proceed
On Python 3, hasattr() calls getattr(): it returns True if getattr()
succeeds, False if getattr() raises an AttributeError, or passes
through the exception, if getattr() failed for a different reason.
On Python 2, hasattr() also calls getattr(), but it catches *any*
exception.
This change replaces hasattr() with getattr(), and it only catches
AttributeError as Python 3, so passes through sqlalchemy exceptions.
Add an unit test to test the new behaviour.
Closes-Bug: #1469225
Change-Id: If9c3ccc03f1dc9746936b0b83ea132508491e577
2e79681670