Fixes #221 - Account for changes in choices field

NetBox 2.7 changes the structure of the objects returned in choice
fields temporarily until v2.8 is released. This PR causes these fields
to serialize to `value` when both `id` and `value` fields are present.

pynetbox/core/response.py

@@ -25,8 +25,7 @@ def get_return(lookup, return_fields=None):
     """Returns simple representations for items passed to lookup.
 
     Used to return a "simple" representation of objects and collections
-    sent to it via lookup. If lookup is an IPNetwork object immediately
-    return the string representation. Otherwise, we look to see if
+    sent to it via lookup. Otherwise, we look to see if
     lookup is a "choices" field (dict with only 'id' and 'value')
     or a nested_return. Finally, we check if it's a Record, if
     so simply return a string. Order is important due to nested_return
@@ -41,6 +40,10 @@ def get_return(lookup, return_fields=None):
             return lookup[i]
         else:
             if hasattr(lookup, i):
+                # check if this is a "choices" field record
+                # from a NetBox 2.7 server.
+                if sorted(dict(lookup)) == sorted(["id", "value", "label"]):
+                    return getattr(lookup, "value")
                 return getattr(lookup, i)
 
     if isinstance(lookup, Record):

tests/unit/test_response.py

@@ -112,6 +112,43 @@ def test_dict(self):
         test = Record(test_values, None, None)
         self.assertEqual(dict(test), test_values)
 
+    def test_choices_idempotence_prev27(self):
+        test_values = {
+            "id": 123,
+            "choices_test": {
+                "value": 1,
+                "label": "test",
+            },
+        }
+        test = Record(test_values, None, None)
+        test.choices_test = 1
+        self.assertFalse(test._diff())
+
+    def test_choices_idempotence_v27(self):
+        test_values = {
+            "id": 123,
+            "choices_test": {
+                "value": "test",
+                "label": "test",
+                "id": 1,
+            },
+        }
+        test = Record(test_values, None, None)
+        test.choices_test = "test"
+        self.assertFalse(test._diff())
+
+    def test_choices_idempotence_v28(self):
+        test_values = {
+            "id": 123,
+            "choices_test": {
+                "value": "test",
+                "label": "test",
+            },
+        }
+        test = Record(test_values, None, None)
+        test.choices_test = "test"
+        self.assertFalse(test._diff())
+
     def test_hash(self):
         endpoint = Mock()
         endpoint.name = "test-endpoint"