Maas set default kernel

  Set the default minimum kernel version used on all new and commissioned nodes.
  to hwe-16.04 => linux-signed-image-generic-hwe-16.04

Related-Bug: PROD-19649 (PROD:19649)

Change-Id: I8340049f906ed284a60aa4ef5416a923f9d6c4b0
diff --git a/maas/region/single.yml b/maas/region/single.yml
index 7c57d9e..3569fff 100644
--- a/maas/region/single.yml
+++ b/maas/region/single.yml
@@ -42,4 +42,5 @@
         ntp_external_only: true
         upstream_dns: ${_param:dns_server01}
         enable_http_proxy: false
-        default_min_hwe_kernel: ''
+        # linux-signed-image-generic-hwe-16.04
+        default_min_hwe_kernel: 'hwe-16.04'