Skip dropping a non-existent temp ECOC collection in the compact coordinator

It is possible that the kDropTempCollection phase of the compaction coordinator may get restarted even if it has already dropped the ecoc.compact temp collection in a previous run. In this case, it will throw a CollectionUUIDMismatch error, instead of returning the result of the actual compaction operation.

A check needs to be performed before the call to drop for the existence of the collection with the specified UUID. If it exists, then skip the drop operation.