Add -s option for neutron metering rules

While adding iptables rule, cidr is added as destination for both ingress
and egress directions. Modified code to add -s for egress and -d for ingress.

Closes-bug: 1310589

Conflicts:
        neutron/tests/unit/services/metering/drivers/test_iptables_driver.py

Change-Id: Id9ca10855e6527d4bec689f8f9bcd6f681221954
(cherry-picked from commit 72e8b5dc5a5e36722327efca4c399f0321e9bbbb)
Merge "Add -s option for neutron metering rules" into stable/icehouse