Summary:
Fix `DisableManualCompaction()` has to wait scheduled manual compaction to start the execution to cancel the job.
When a manual compaction in thread-pool queue is cancel, set the job is_canceled to true and clean the resource.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9557
Test Plan: added unittest that will hang without the change
Reviewed By: ajkr
Differential Revision: D34214910
Pulled By: jay-zhuang
fbshipit-source-id: 89dbaee78ddf26eb13ce862c2b15f4a098b36a78