CI: Add Ubuntu 20.04 docker packer job

Change-Id: I3493f6b3d4473656e169eabb9036ee1c380b2316
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>
diff --git a/jjb/ci-management/ci-packer.yaml b/jjb/ci-management/ci-packer.yaml
index 74f1381..5e2488e 100644
--- a/jjb/ci-management/ci-packer.yaml
+++ b/jjb/ci-management/ci-packer.yaml
@@ -45,3 +45,4 @@
       - centos-cs-8
       - centos-cs-9
       - ubuntu-18.04
+      - ubuntu-20.04