utils: make idp parameter to get_adapters() optional, return concatenation of default an specific adapters

mellon/utils.py

@@ -93,9 +93,9 @@ def import_object(path):
     return getattr(module, name)
 
 @to_list
-def get_adapters(idp):
+def get_adapters(idp={}):
     idp = idp or {}
-    adapters = idp.get('ADAPTER') or app_settings.ADAPTER
+    adapters = idp.get('ADAPTER', []) + app_settings.ADAPTER
     for adapter in adapters:
         yield import_object(adapter)()