Fix typo in the find_pool deprecated rule
Fix typo in the find_pool deprecated rule

The find_pool policy was referencing find_pools, which was incorrect and
caused oslo.policy to think the rule name was changing, which isn't the
case. This commit updates the deprecated rule to use the proper policy
name.

Change-Id: Iaac9b2c14e118056e1cb11ad3b1fa18b07eb22ac

openstack/designate,openstack/designate,openstack/designate