Retry event actions

There are some race conditions between some actions like updating while starting. The lease status checker (implemented in the state-machine blueprint) denies the following actions if the lease is at the transitional status and it works well for most of cases.

However, the following scenarios are not acceptable.

* Starting while creating: the start action is denied and the start_lease event status becomes ERROR.
* Starting while updating: the start action is denied and the start_lease event status becomes ERROR.
* Terminating while updating: the terminate action is denied and the end_lease event status becomes ERROR.

To prevent these events from being ERROR, start_lease and end_lease would be better to be retried after an interval.