Fix devstack to support the new pulled out swift3

Change-Id: Ia4f5092e666b581aab4af4851c2848e84817c07a
diff --git a/files/swift/proxy-server.conf b/files/swift/proxy-server.conf
index 2fe20f5..84bf9cd 100644
--- a/files/swift/proxy-server.conf
+++ b/files/swift/proxy-server.conf
@@ -40,7 +40,7 @@
 admin_password = %SERVICE_PASSWORD%
 
 [filter:swift3]
-use = egg:swift#swift3
+use = egg:swift3#middleware
 
 [filter:tempauth]
 use = egg:swift#tempauth