Make get_object_by_id() work for most Django objects.

Django object id is usually an int while lookup is an unicode string.
It works for Openstack but not other Django objects.

This patch makes other standard Django apps reusing Horizon easier.

Change-Id: I436c34e8b17340537f8d201001741d34c933764e
Merge "Make get_object_by_id() work for most Django objects."