Adding ad[4-6]s* to default devices

[Chris Turner]

Matthew Dillon wrote:
> 
>     We should be creating them through ad7 already.  Check HEAD.  If it isn't
>     doing it properly then we definitely want to adjust it.
> 

Okay - I think I asked my question incorrectly based on the (bad)
assumption that this was being done for the lower numbered 'ad' units..

I meant if we should add partition devices to more slices, e.g:

ad4s0[a-p] is present, s1[a-p] is present, but s2 - s4 only have the
'whole slice' device

current HEAD policy creates "{ad[1-7]s[01][a-p],ad[1-7]s[0-4]}"