[k8s] Adjust externaldns test functions

- Use ctl hostname instead of k8s.kube_host due kube_host
is an ip address of keepalived k8s api.
- Discover ctl with specific role 'k8s_controller'
- Fix nit with awk field
- Fix nit with format fields

User-Story:https://mirantis.jira.com/browse/PROD-12826

Change-Id: I52d89b4d3994338a800eed4f6b5555cad6bdedc8
diff --git a/tcp_tests/helpers/ext.py b/tcp_tests/helpers/ext.py
index f7b8005..99baaff 100644
--- a/tcp_tests/helpers/ext.py
+++ b/tcp_tests/helpers/ext.py
@@ -26,6 +26,7 @@
     'salt_master',
     'salt_minion',
     'k8s_virtlet',
+    'k8s_controller',
     'decapod_mon',
     'decapod_osd',
     'decapod_all',