Improve handling of $ref in swagger files

It turns out that swagger merges $refed attributes with those defined inline,
so do the same here.

templating/matrix_templates/units.py

@@ -36,14 +36,18 @@ logger = logging.getLogger(__name__)
 
 def resolve_references(path, schema):
     if isinstance(schema, dict):
-        result = {}
-        for key, value in schema.items():
-            if key == "$ref":
+        # do $ref first
+        if '$ref' in schema:
+            value = schema['$ref']
             path = os.path.join(os.path.dirname(path), value)
             with open(path) as f:
-                    schema = yaml.load(f)
-                return resolve_references(path, schema)
+                ref = yaml.load(f)
+            result = resolve_references(path, ref)
+            del schema['$ref']
         else:
+            result = {}
+
+        for key, value in schema.items():
             result[key] = resolve_references(path, value)
         return result
     elif isinstance(schema, list):