Disable test_rescued_vm_attach_volume

To fix bug 1126187, we are forbidding attach/detach in rescue mode.
Which test_rescued_vm_attach_volume explicitly checks for.

Change-Id: I745ccb9c7bc763809efd617eadfe5fd2fab1cb48
diff --git a/tempest/tests/compute/servers/test_server_rescue.py b/tempest/tests/compute/servers/test_server_rescue.py
index 70e3b7c..7e79bbd 100644
--- a/tempest/tests/compute/servers/test_server_rescue.py
+++ b/tempest/tests/compute/servers/test_server_rescue.py
@@ -136,6 +136,7 @@
                           self.image_ref_alt)
 
     @attr(type='positive')
+    @testtools.skip("Skipped due to BUG:1126187")
     def test_rescued_vm_attach_volume(self):
         client = self.volumes_extensions_client