Correct skip condition for migrate_server

CONF.compute_feature_enabled.cold_migration should be checked
for migrate_server, this is to use the right skip condition
for migrate_server.

Change-Id: Iab825968861a867c788930f3ce27c62cd2323d3c
diff --git a/tempest/api/compute/admin/test_servers_negative.py b/tempest/api/compute/admin/test_servers_negative.py
index b0f18d7..ca53696 100644
--- a/tempest/api/compute/admin/test_servers_negative.py
+++ b/tempest/api/compute/admin/test_servers_negative.py
@@ -124,8 +124,8 @@
                           data_utils.rand_uuid())
 
     @decorators.idempotent_id('b0b17f83-d14e-4fc4-8f31-bcc9f3cfa629')
-    @testtools.skipUnless(CONF.compute_feature_enabled.resize,
-                          'Resize not available.')
+    @testtools.skipUnless(CONF.compute_feature_enabled.cold_migration,
+                          'Cold migration not available.')
     @testtools.skipUnless(CONF.compute_feature_enabled.suspend,
                           'Suspend is not available.')
     @decorators.attr(type=['negative'])