The current `List()` implementation just lists the DNS resorce records in
a given managed zone once and retruns the list. It neither performs a paged
walk nor does it consider the `page_token` in the returned response.
This change walks all the pages and aggregates the records in the pages
and returns the aggregated list. This is potentially dangerous as it can
blow up memory if there are a huge number of records in the given
managed zone. But this is the best we can do without changing the
provider interface too much. Next step is to define a new paged list
interface and implement it.
There can be multiple DNS resource records for a given name. They can
vary by type, ttl, rrdata and a number of various other parameters. It
is incorrect to return a single resource record for a given name.
This change updates the Get interface to return multiple records for a given
name and uses this list in the federated service controller to perform
DNS operations.
