Negative test for rescuing a non-existent server

Added a negative test for rescuing a server
which does not exist.

Change-Id: I618f8f59ad455c48b76fed4c0f836e4e9e49c736
diff --git a/tempest/api/compute/servers/test_server_rescue.py b/tempest/api/compute/servers/test_server_rescue.py
index 8225a4c..13c2f74 100644
--- a/tempest/api/compute/servers/test_server_rescue.py
+++ b/tempest/api/compute/servers/test_server_rescue.py
@@ -126,6 +126,13 @@
                           self.rescue_id, 'HARD')
 
     @attr(type=['negative', 'gate'])
+    def test_rescue_non_existent_server(self):
+        # Rescue a non-existing server
+        self.assertRaises(exceptions.NotFound,
+                          self.servers_client.rescue_server,
+                          '999erra43')
+
+    @attr(type=['negative', 'gate'])
     def test_rescued_vm_rebuild(self):
         self.assertRaises(exceptions.Duplicate,
                           self.servers_client.rebuild,