Skip test_server_connectivity_cold_migration_revert until fixed

We're having a hard time landing changes like
https://review.openstack.org/#/c/601830/ due to
persistent intermittently failing tests that are
not getting attention to resolve, so this skips
one of those tests until the bug is fixed.

Change-Id: I7c2080acbcd47b9fb1deefd30d427f3e4076ea39
Related-Bug: #1788403
diff --git a/tempest/scenario/test_network_advanced_server_ops.py b/tempest/scenario/test_network_advanced_server_ops.py
index 8827610..e94ce3d 100644
--- a/tempest/scenario/test_network_advanced_server_ops.py
+++ b/tempest/scenario/test_network_advanced_server_ops.py
@@ -230,6 +230,7 @@
 
         self.assertNotEqual(src_host, dst_host)
 
+    @decorators.skip_because(bug='1788403')
     @decorators.idempotent_id('25b188d7-0183-4b1e-a11d-15840c8e2fd6')
     @testtools.skipUnless(CONF.compute_feature_enabled.cold_migration,
                           'Cold migration is not available.')