Upgrade Helm version to 2.15 for COMAC pod

Helm 2.15 is required for resolve nested chart dependencies.

Change-Id: Idd6b518ae55c34b84d6a8c2310611d5725a80ed5
diff --git a/deployment-configs/comac-onf-testbed-kubespray.yaml b/deployment-configs/comac-onf-testbed-kubespray.yaml
index 4f60bbd..20479ee 100644
--- a/deployment-configs/comac-onf-testbed-kubespray.yaml
+++ b/deployment-configs/comac-onf-testbed-kubespray.yaml
@@ -54,4 +54,4 @@
 
 helm_enabled: true
 helm_deployment_type: host
-helm_version: v2.14.2
+helm_version: v2.15.0