Enable to apply policies to resources with special plural

Enable to apply policies to resources with special plural

Some neutron resource with special plural form
can not apply the policy control using policy.json
when create/update/delete the resource.
Following resources can not apply the policy control
because of wrong pluralize process:

  * firewall_policy
  * ipsec_policy
  * ikepolicy

Current pluralize process is as following:
  "resource" + "s"
  e.g. *_policy -> *_policys

This fix enables to apply the policy control with those resources.
  *_policy -> *_policies

Change-Id: I38a55e95f653f69edd477dbbcbdd6e956c0a0e2b
Closes-Bug: 1407886