Updated openstack/openstack
Project: openstack/oslo.db  9000db08b8b03f210980190e0d375c4e5a955ce1

Allow usage of several iterators on ModelBase

Storing iterator object as attribute of model doesn't allow
to use several iterators at the same time

Now the new Iterator object which is created by iter()
stores model object, and in such way several iterators can be
created and work without interfering

Change-Id: I5806877a2d15d449b948307a522bf2fb56bf8110