stateShutdownPrepare is supposed to inform driver that it will be closed soon
so that the driver can prepare and finish all background threads quickly on
stateShutdownWait call.
Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy@virtuozzo.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>