qemu-img: fix error reporting for -object

qemu-img: fix error reporting for -object

Error reporting for user_creatable_add_opts_foreach was changed so that
it no longer called 'error_report_err' in:

  commit 7e1e0c11127bde81cff260fc6859690435c509d6
  Author: Markus Armbruster <armbru@redhat.com>
  Date:   Wed Oct 17 10:26:43 2018 +0200

    qom: Clean up error reporting in user_creatable_add_opts_foreach()

Some callers were updated to pass in "&error_fatal" but all the ones in
qemu-img were left passing NULL. As a result all errors went to
/dev/null instead of being reported to the user.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>