Add Volume#parent_whole_disk.

Add a method to access the disk containing a given volume.
The method returns a Device object.
Use Volume#parent_whole_disk in :clone task.
Re-attach the source volume before copying.

For some reason that is not entirely clear to me, after running some programs (for example, xar),
the creation dates *in the source* are modified. To prevent this or other potential modifications
of the source volumes when copying or cloning, it is necessary to re-attach
the source volume in read-only mode. Only remounting the volume in read-only mode
does not seem sufficient (why?).
Refactor code to reattach disk.
Reattach a disk in rw mode if needed in :fill task.