Allow control_exchange override

With the quantum to neutron name change, this could be useful in
some cases.
This change is dependent on Common change:
  https://review.openstack.org/#/c/84757/

Change-Id: Id3d9474332917571b692f3bba8fed4ca4ac1745a
Closes-Bug: #1259038
Remove policy json file

Remove the policy.json template, as they contain no templated variables.
This would allow use of the policy.json files provided via the package,
and decrease the need to sync them with upstream

Change-Id: Iad2562d54907d8987c93c2ee41147a1027f57a69
Implements: blueprint remove-policy-templates
Merge "Allow control_exchange override"
Merge "Remove policy json file"