qapi: Turn ShutdownCause into QAPI enum

Needed so the patch after next can add ShutdownCause to QMP events
SHUTDOWN and RESET.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Message-Id: <20181205110131.23049-2-d.csapak@proxmox.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
2 files changed