Replace six.itervalues with dict.values()
Replace six.itervalues with dict.values()

We should avoid using six.itervalues to achieve iterators.
We can use dict.values instead, as it willreturn iterators
in PY3 as well. And dict.items/values will more
readable.

Change-Id: Ic9a0fe2edd939ca28bdc634f5ee92ec2546ddd29

openstack/vitrage,openstack/vitrage,openstack/vitrage