Ensure git cronjob absent for correct user

When removing a cron resource by setting it absent, it must continue
to specify the user if it wasn't root (the default) since crontabs
are per-user files.

Change-Id: Id68051821b0cca8bbf3e90446f5d915ac9d32be4

manifests/cron.pp

@@ -15,6 +15,7 @@ class gerrit::cron (
 
   cron { 'gerrit_repack':
     ensure => absent,
+    user   => 'gerrit2',
   }
   cron { 'optimize_git_repo':
     user        => 'gerrit2',
@@ -29,6 +30,7 @@ class gerrit::cron (
   if $replicate_local {
     cron { 'mirror_repack_local':
       ensure => absent,
+      user   => 'gerrit2',
     }
     cron { 'optimize_git_repo_local_replication':
       user        => 'gerrit2',