QEMU will abort() for the reasons now:
invalid runstate transition: 'prelaunch' -> 'postmigrate'
Aborted
This happens when:
|<- watchdog timeout happened, then sets reset_requested to
| SHUTDOWN_CAUSE_GUEST_RESET;
|<- hot-migration thread sets vm state to RUN_STATE_FINISH_MIGRATE
| before the last time of migration;
|<- main thread gets the change of reset_requested and triggers
| reset, then sets vm state to RUN_STATE_PRELAUNCH;
|<- hot-migration thread sets vm state to RUN_STATE_POSTMIGRATE.
Then 'prelaunch' -> 'postmigrate' runstate transition will happen.
It is legal so add this transition to runstate_transitions_def.
Signed-off-by: Jinhua Cao <caojinhua1@huawei.com>