Created DiskReportRunner class.

This class will handle reporting like the GarbageCollector class
does for garbage collection.

Adapted the interface of scheduler and ArchiveRequests to allow delegating
reporting to the disk report runner.

This commit is not functionnal. We still need to:
- Implement the ToReport/Failed queues interface.
- Adapt the queueing in the scheduler/ArchiveMount
- Implement the popping of jobs to report.
- Implement the async reporter for the files.
- Develop the user interface for failed requests.