Add a 'loglevel' variable to values files

Example of changing the log level when loading a chart:

    helm install --set loglevel=INFO --name voltha voltha

Change-Id: I277610758b79ea3bcf083899d9dfcf28b32e9e0c
diff --git a/voltha/values.yaml b/voltha/values.yaml
index 6237196..319685e 100644
--- a/voltha/values.yaml
+++ b/voltha/values.yaml
@@ -54,6 +54,9 @@
 kafkaReleaseName: cord-kafka
 etcdReleaseName: etcd-cluster
 
+
+loglevel: "DEBUG"
+
 images:
   vcore:
     repository: 'voltha/voltha-voltha'