Issue:
In FileCopyBasedInitialSyncer::_cloneFiles, we can have a deadlock while acquiring FileCopyBasedInitialSyncer::_mutex between the main asyncTry and the return future.

I assume that can happen if the startClonerFuture is ready before we hit the return statement.

Proposed fix:

The lock in the main asyncTry needs to be scoped to include only state's changing lines and not to include the return statement.

Needed for better debugging:

Can we add also a log line in the begging of FileCopyBasedInitialSyncer::_cloneFiles to output the number of files in filesToClone