Improve checking and creating Azure DNS Zones

This change improves the process for checking for AzureDNS zones by using the known set and not relying upon custom error handling.

Since the provider already fetches the zones, octodns doesn't need to make a second call to check for the existence of the zone - _populate_zones already does that for us.

tests/test_octodns_provider_azuredns.py

@@ -498,32 +498,42 @@ class TestAzureDnsProvider(TestCase):
         record_list = provider._dns_client.record_sets.list_by_dns_zone
         record_list.return_value = rs
 
+        zone_list = provider._dns_client.zones.list_by_resource_group
+        zone_list.return_value = [zone]
+
         exists = provider.populate(zone)
-        self.assertTrue(exists)
+        
         self.assertEquals(len(zone.records), 17)
+        self.assertTrue(exists)
 
     def test_populate_zone(self):
         provider = self._get_provider()
 
         zone_list = provider._dns_client.zones.list_by_resource_group
-        zone_list.return_value = [AzureZone(location='global'),
-                                  AzureZone(location='global')]
+        zone_1 = AzureZone(location='global')
+        # This is far from ideal but the zone constructor doesn't let me set it on creation
+        zone_1.name = "zone-1"
+        zone_2 = AzureZone(location='global')
+        # This is far from ideal but the zone constructor doesn't let me set it on creation
+        zone_2.name = "zone-2"
+        zone_list.return_value = [zone_1,
+                                  zone_2,
+                                  zone_1]
 
         provider._populate_zones()
 
-        self.assertEquals(len(provider._azure_zones), 1)
+        # This should be returning two zones since two zones are the same
+        self.assertEquals(len(provider._azure_zones), 2)
 
     def test_bad_zone_response(self):
         provider = self._get_provider()
 
         _get = provider._dns_client.zones.get
         _get.side_effect = CloudError(Mock(status=404), 'Azure Error')
-        trip = False
-        try:
-            provider._check_zone('unit.test', create=False)
-        except CloudError:
-            trip = True
-        self.assertEquals(trip, True)
+        self.assertEquals(
+            provider._check_zone('unit.test', create=False), 
+            None
+        )
 
     def test_apply(self):
         provider = self._get_provider()