Designate no longer uses the parameters in the [backend:bind9] section, since ppols.yaml was introduced. This change ensures the parameters in this wrong section are purged. Also, this change introduces support for setting up backend using pools.yaml according to the current installation guide. Closes-Bug: #1961516 Change-Id: I28a91ab99325970db1e96aa904f35e8f9a5e109c