Delete all user-creatable objects in /objects when exiting QEMU, so they
can perform cleanup actions.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170824192315.5897-2-ehabkost@redhat.com>
Acked-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Zack Cornelius <zack.cornelius@kove.net>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>