Get and store the map of resource records to domain names that
        point to them.

def get_route53_records(self):
        ''' Get and store the map of resource records to domain names that
        point to them. '''

        r53_conn = route53.Route53Connection()
        all_zones = r53_conn.get_zones()

        route53_zones = [ zone for zone in all_zones if zone.name[:-1]
                          not in self.route53_excluded_zones ]

        self.route53_records = {}

        for zone in route53_zones:
            rrsets = r53_conn.get_all_rrsets(zone.id)

            for record_set in rrsets:
                record_name = record_set.name

                if record_name.endswith('.'):
                    record_name = record_name[:-1]

                for resource in record_set.resource_records:
                    self.route53_records.setdefault(resource, set())
                    self.route53_records[resource].add(record_name)