Juno neutron updates

The following changes are needed to get neutron functional in Juno.

* ipset needs to be enabled in the l3 agent securitygroup section.
* conntrack needs to be installed.
* iputils-arping needs to be installed.
* policy json needs to be updated.

This PR adds all of the required changes to neutron and resolves
issue: https://github.com/rcbops/ansible-lxc-rpc/issues/276