Replace context decorators with context managers

The context decorator needs to have the "context" parameter in the
first position or the first argument must be "self" or "cls",
followed by the "context" object.

Closes-Bug: #2017784
Change-Id: Ib80f7c72e78854226b227e354792320c78fed5d0
(cherry picked from commit 4e27e27)

neutron/objects/db/api.py

@@ -30,19 +30,19 @@ def _get_filter_query(obj_cls, context, query_field=None, query_limit=None,
     return query
 
 
-@db_api.CONTEXT_READER
 def get_object(obj_cls, context, **kwargs):
-    return _get_filter_query(obj_cls, context, **kwargs).first()
+    with db_api.CONTEXT_READER.using(context):
+        return _get_filter_query(obj_cls, context, **kwargs).first()
 
 
-@db_api.CONTEXT_READER
 def count(obj_cls, context, query_field=None, query_limit=None, **kwargs):
-    if not query_field and obj_cls.primary_keys:
-        query_field = obj_cls.primary_keys[0]
-        if query_field in obj_cls.fields_need_translation:
-            query_field = obj_cls.fields_need_translation[query_field]
-    return _get_filter_query(obj_cls, context, query_field=query_field,
-                             query_limit=query_limit, **kwargs).count()
+    with db_api.CONTEXT_READER.using(context):
+        if not query_field and obj_cls.primary_keys:
+            query_field = obj_cls.primary_keys[0]
+            if query_field in obj_cls.fields_need_translation:
+                query_field = obj_cls.fields_need_translation[query_field]
+        return _get_filter_query(obj_cls, context, query_field=query_field,
+                                 query_limit=query_limit, **kwargs).count()
 
 
 def _kwargs_to_filters(**kwargs):