error: Clean up abuse of error_report() for help

Use error_printf() instead, so the help gets presented more nicely.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-id: 1360354939-10994-3-git-send-email-armbru@redhat.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>