smartd Selective Self-Test SIZE

[alzheimer]

As requested a separate ticket from #301

• If possible I'd like to be able to specify the SIZE directly in smartd.conf the same way it's possible to do on the command line (-t select,cont+SIZE). Ideally this should also remove the need of running the first select test manually.

• It would be cool if SIZE could be specified as a percentage, so for example a DEFAULT entry that checks 5% of a disk could be made regardless of disk sizes.