Replace all Ubuntu 16.04 with Ubuntu18.04 image

Change-Id: I86b84957145f7c1f253d3158e42e015c322788eb
diff --git a/jjb/verify/voltha-openonu-adapter-go.yaml b/jjb/verify/voltha-openonu-adapter-go.yaml
index 4746e97..b66aaa6 100644
--- a/jjb/verify/voltha-openonu-adapter-go.yaml
+++ b/jjb/verify/voltha-openonu-adapter-go.yaml
@@ -28,14 +28,14 @@
           unit-test-targets: 'lint sca'
           unit-test-keep-going: 'true'
           junit-allow-empty-results: true
-          build-node: 'ubuntu16.04-basebuild-4c-8g'
+          build-node: 'ubuntu18.04-basebuild-4c-8g'
       - 'make-unit-test':
           dest-gopath: "github.com/opencord"
           name-extension: "-tests"
           unit-test-targets: 'test'
           unit-test-keep-going: 'true'
           junit-allow-empty-results: true
-          build-node: 'ubuntu16.04-basebuild-2c-4g'
+          build-node: 'ubuntu18.04-basebuild-2c-4g'
 
 - job-group:
     name: 'verify-voltha-openonu-adapter-go-jobs-voltha-2.7'