Update PTR Record example
Update PTR Record example

* 192.0.2.12 --> example.org.
* example.org. --> 192.0.2.12
* RPC 12.2.0.192.in-addr.arpa.

Change-Id: I609983a5f66614aeba36da63ac9a8446c70b4e18

openstack/designate,openstack/designate,openstack/designate