kern/149523: [geom] label tasting hangs during boot

[Bengt Ahlgren]

I did some testing with wiping the first 100 sectors, but that did not
make any difference.

It does look like the IO isn't completing, suggesting an interrupt
problem.  Indeed, disabling the apic (set hint.apic.0.disabled=1 at
the loader prompt) solves the tasting issue!

But strangely enough, another Thinkpad X40 I tried did not need
hint.apic.0.disabled=1 to boot from the same 8.1-REL install media.
Hmm, I start to suspect hardware problems, or an old BIOS.  Another
issue with the problematic X40 is that it fails to mount the install
DVD in fixit mode.

So, lets close this PR - the problem seems to be due to faulty
hardware.

Bengt