Make POD's node selector can configure in values.yaml

Change-Id: Ia6b4588546fda60ea2cd9ec581a017826cac9f66
diff --git a/mcord/mcord-control-plane/templates/cassandra.yaml b/mcord/mcord-control-plane/templates/cassandra.yaml
index 312233b..cdb827c 100644
--- a/mcord/mcord-control-plane/templates/cassandra.yaml
+++ b/mcord/mcord-control-plane/templates/cassandra.yaml
@@ -46,7 +46,7 @@
         app: cassandra
     spec:    
       nodeSelector:
-       kubernetes.io/hostname: "node3"
+       kubernetes.io/hostname: "{{ .Values.hssdb_node_selector }}"
       terminationGracePeriodSeconds: 1
       containers:
       - name: cassandra