This way we use the "normal" way of printing errors for hmp commands.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>