Replace g.next() with next(g)
Replace g.next() with next(g)

In Python 3, g.next() has been renamed to g.__next__().
The next() buildin function will work fine for Python 2&3.

Partial implements: blueprint py33-support
Change-Id: I992d019eb180f514388f21b2400b51c94c7bdad5

Tesora/tesora-python-troveclient,metacloud/python-troveclient,openstack/python-troveclient,openstack/python-troveclient,metacloud/python-troveclient,Tesora/tesora-python-troveclient