Race in cancelling compactions

seems we might have a race situation when cancelling compactions

currently we do the following to ensure that we don't start any new compactions when we try to do markAllCompacting()

1. pause compactions - this makes sure we don't create any new compaction tasks from the compaction strategies
2. cancel any ongoing compactions - compactions register themselves with the CompactionMetrics and then, when cancelling we get all compactions here, and tell them to stop

Problem is that there is a window between when the CompactionTask is created and when it is registered in CompactionMetrics meaning with a bit of bad luck, we could have a situation like this:

1. we finish a compaction and create a new CompactionTask from the compaction strategy
2. we pause the compaction strategies to not create any new CompactionTasks
3. we cancel all ongoing compactions
4. The CompactionTask created in #1 above registers itself in CompactionMetrics and misses that it should be cancelled