R1:e9af4f897079

Fix an issue where Drydock followup tasks would not queue if the main task failed

Summary:
Ref T9994. This fixes the first issue discussed on that task, which is that when a merge fails after "arc land", we would not clean up all the leases properly.

Specifically, when a merge fails, we use `queueTask()` to schedule a followup task. This followup destroys the lease and frees the underlying resource.

However, the default behavior of `queueTask()` is to //not queue tasks// if the parent task fails. This…