puppet: Fix exceptions with multiple certbot declarations.

Since 9e8f1aacb3, zulip_ops machines
might have two Package declarations for `certbot`, which doesn't work
in puppet.

The fix is, as usual, to use our `zulip::safepackage` wrapper instead.

puppet/zulip_ops/manifests/base.pp

@@ -35,7 +35,7 @@ class zulip_ops::base {
     'git',
     'nagios-plugins-contrib',
   ]
-  package { $org_base_packages: ensure => 'installed' }
+  zulip::safepackage { $org_base_packages: ensure => 'installed' }
 
   # Add system users here
   $users = []