Add gnupg2 install for zypper as well

As of today zypper is explicitly using /usr/bin/gpg2 for signature
validation but this is typically not installed on an Ubuntu host
because it defaults to gnupg (1.x, which only provides /usr/bin/gpg).

This change is needed so that the zypper-minimal element has a
chance of working on a Xenial host.

Change-Id: If57b07dcf31b8eeb2a3a44442315dd1d70b3523d

manifests/init.pp

@@ -47,7 +47,9 @@ class diskimage_builder (
 
   # Ubuntu trusty doesn't support zypper today, so skip it.
   if ($::lsbdistcodename != 'trusty') {
-    package { 'zypper':
+    # gnupg2 is a missing dependency on zypper, see
+    # https://bugs.launchpad.net/bugs/1639428
+    package { ['zypper', 'gnupg2']:
       ensure => present,
     }
   }