Minor fixes in k8s tests

- Fix test_k8s_externaldns_coredns test
- Fix K8SSampleDeployment class

Change-Id: I4734e3987af5495c9eb9f4dda4fedd7153964cb6
diff --git a/tcp_tests/tests/system/test_k8s_actions.py b/tcp_tests/tests/system/test_k8s_actions.py
index 6510a67..b75d59c 100644
--- a/tcp_tests/tests/system/test_k8s_actions.py
+++ b/tcp_tests/tests/system/test_k8s_actions.py
@@ -65,7 +65,9 @@
         })
 
         show_step(5)
-        k8s_deployed.nslookup(hostname, svc.get_ip())
+        dns_svc = k8s_deployed.api.services.get(
+            name='coredns', namespace='kube-system')
+        k8s_deployed.nslookup(hostname, dns_svc.get_ip())
 
         show_step(6)
         deployment.delete()