fix the confused issue in server_client about list_server

make list_serve use the correct the url in xml/server_client
and refactor the test_list_server_filters.py

fix bug 1153467

Change-Id: I21165050cee22b5530df0bb834de810906487636
diff --git a/tempest/services/compute/xml/servers_client.py b/tempest/services/compute/xml/servers_client.py
index 655a345..fceeb28 100644
--- a/tempest/services/compute/xml/servers_client.py
+++ b/tempest/services/compute/xml/servers_client.py
@@ -160,7 +160,7 @@
         return array
 
     def list_servers(self, params=None):
-        url = 'servers/detail'
+        url = 'servers'
         if params:
             url += '?%s' % urllib.urlencode(params)