Update kubectl veraion to 1.15.11

Issue-ID: CIMAN-33 IT-19647
Change-Id: I4bb6667b952aa99adb916f6a2c7b54a668d849c9
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>
diff --git a/packer/provision/helm.yaml b/packer/provision/helm.yaml
index 6b000c3..daecffe 100644
--- a/packer/provision/helm.yaml
+++ b/packer/provision/helm.yaml
@@ -6,7 +6,7 @@
   become_method: sudo
 
   vars:
-    kubectl_version: 1.11.2
+    kubectl_version: 1.15.11
     helm_version: 2.16.6
 
   tasks: