Migrate to ARM Ubuntu18.04 node

Ubuntu 16.04 still has SSH and Kernel issues.
Migrating to Ubuntu18.04 since we have a good
instance now.

TODO: Disable Ubuntu16.04 arm nodes.
- Currently Ubuntu18.04 arm nodes are under more test.
- No additional costs since no job is using 16.04 arm
  nodes.
- Once confirmed, these will be disabled.

Change-Id: I1ef6dfc04aa6e85531f824e24ad517137a7080ca
Issue-ID: CIMAN-33
Signed-off-by: Jessica Wagantall <jwagantall@linuxfoundation.org>
diff --git a/jjb/vnfsdk/vnfsdk-refrepo.yaml b/jjb/vnfsdk/vnfsdk-refrepo.yaml
index d94f8cb..58a45d1 100644
--- a/jjb/vnfsdk/vnfsdk-refrepo.yaml
+++ b/jjb/vnfsdk/vnfsdk-refrepo.yaml
@@ -51,7 +51,7 @@
 #    mvn-settings: 'vnfsdk-refrepo-settings'
 #    files: '**'
 #    archive-artifacts: ''
-#    build-node: ubuntu1604-docker-arm64-4c-2g
+#    build-node: ubuntu1804-docker-arm64-4c-2g
 #
 - project:
     name: vnfsdk-refrepo-sonar