[SDFAB-189] Update ONOS CI and test new image

This is the part 1 (other changes will follow).
Use new ubuntu 20.04 based executor for bazel-verify jobs

Change-Id: Ifbaa21a50657ed0864a87b0962a1c7cc826d00c0
diff --git a/jjb/onos/onos-verify.yaml b/jjb/onos/onos-verify.yaml
index ab312a8..d524e89 100644
--- a/jjb/onos/onos-verify.yaml
+++ b/jjb/onos/onos-verify.yaml
@@ -713,7 +713,7 @@
     project: onos
 
     build-timeout: '30'
-    build-node: 'ubuntu16.04-basebuild-8c-15g'
+    build-node: 'ubuntu20.04-basebuild-8c-15g'
 
     stream:
       - 'master'