Update Jenkins executors to Ubuntu 18.04

- Upgrade global jjb to v0.57.4
- Upgrade packer to v0.7.0
- Use the Ansible approach to install most required services

Change-Id: I1a56db63e14d847971131eef96828004c6ae4478
diff --git a/packer/provision/install-base-pkgs-Ubuntu.yaml b/packer/provision/install-base-pkgs-Ubuntu.yaml
new file mode 100644
index 0000000..2ab6308
--- /dev/null
+++ b/packer/provision/install-base-pkgs-Ubuntu.yaml
@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: 2020 Open Networking Foundation <info@opennetworking.org>
+#
+# SPDX-License-Identifier: LicenseRef-ONF-Member-Only-1.0
+
+---
+- name: Install base packages
+  apt:
+    name:
+      - build-essential
+      - devscripts
+      - dh-systemd
+      - equivs
+      - gdebi
+    state: latest
+  become: yes