Do we actually need to duplicate the whole exec statement here?  Seems like maybe we could reduce the duplication a bit with something along the lines of:

```
$disk_hash = $name
$disk_array = split($disk_hash, ':')
$disk = $disk_array[0]
$disk_journal = $disk_array[1]
if $disk_journal {
  $disk_journal_real = $disk_journal
} else {
  $disk_journal_real = $disk
}
exec { "create osd $disk":
     cwd     => "/home/$user/bootstrap",
     command => "/usr/bin/ceph-deploy --overwrite-conf osd create $::hostname:$disk:$disk_journal_real",
     require => Exec["zap $disk"],
     unless  => "/usr/bin/test -e /home/$user/zapped/$disk",
  }
```

That way if no $disk_journal is specified you end up with the journal on the same disk, but we don't duplicate code for the entire exec.