Repair include_object to accommodate new objects

The tests in tests/sqlalchemy/test_migrations.py which expect
to see changes in unique constraints fail due to the
assumption that the "include_object" feature of Alembic only
deals with the 'table' and 'column' constructs.   As Alembic
0.7.0 has added include_object support for 'index' and
'unique_constraint', this method should not be limiting
itself to not include objects that it's testing for.
Tests won't pass on Alembic 0.7.0 without this patch.

Change-Id: Ia71446bb8c0b248c6310534deb290524e3946987
Make test_models pass on py3

Add a check that models.ModelBase is iterable.
Remove checking on next() method since models.modelBase
isn't actually iterator.
Remove unnecessary checks from TimestampMixinTest

Change-Id: Ibbde0e49bec25e1acddaf64f03083cf46481a581
Merge "Repair include_object to accommodate new objects"
Merge "Make test_models pass on py3"