the same pagination bug that happens for accounts with a large number of
domains also happens for DNS zones with a large number of records. The
previous code assumes that all records are returned in a single page.
Changed the code to do an exact match search so that it returns only the few
required records and never paginates replies.
fixes issue #4956
previous code only worked for the first 10 domains on the account (as Linode
API returned a paginated response, with only 10 records).
This change makes an exact search query for each subdomain, completely removing any
need for walking through paginated responses. What makes it work for large
accounts with any number of domains.