Add 'kern.disks', a sysctl which returns the list of disks from disk_enumerate(), space delimited.  This allows non-root users to get a list of disks and will simplify libdisk's Disk_Names().
Add 'kern.disks', a sysctl which returns the list of disks from
disk_enumerate(), space delimited.  This allows non-root users to get a
list of disks and will simplify libdisk's Disk_Names().

Reviewed by:	phk

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