Fix build issues with Ubuntu 16.04 EC2 image

- Install software-properties-common to fix build
- Update common-packer to newer commit
- Change packer-version to 1.2.4

Change-Id: Ib8ee100b3cfa6f3b0de129106e6e7b229d1d8ca5
diff --git a/packer/provision/baseline.sh b/packer/provision/baseline.sh
index a087efa..e34d7b8 100644
--- a/packer/provision/baseline.sh
+++ b/packer/provision/baseline.sh
@@ -213,8 +213,14 @@
 
     echo "---> Updating operating system"
 
+    # Change made 2018-07-09 by zdw
+    # per discussion on #lf-releng, the upstream Ubuntu image changed to be
+    # missing add-apt-repository, so the next command failed.
+    apt-get update -m
+    apt-get install -y software-properties-common
+
     # add additional repositories
-    sudo add-apt-repository "deb http://us.archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe restricted multiverse"
+    add-apt-repository "deb http://us.archive.ubuntu.com/ubuntu $(lsb_release -sc) main universe restricted multiverse"
 
     echo "---> Installing base packages"
     apt-get clean