Update pools management way

In Mitaka since [1] it is recommended to use pools.yaml
file to manage pools in Designate.

[1] https://github.com/openstack/designate/commit/e612a3974fe6bb411c1a97f0b27186ef7d6c8e0d

Change-Id: I12f0b32fd230c75a52de09e1d49a18e01ab97b03
1 file changed