Default scan incremenet by sector

This has the highest likelyhood to find the disks as default
partitioning is no longer at head or cylinder size but rather at 4k
alignment.
Prefer the reported number of sectors over calculation

The disks no longer abide by the fictitious cylinder/head/sectors
arrangement and the total size of the disk is not a multiplication of
these three approximate numbers so there is no reason to base
validations on the chs values but it's better to use the real size of
the disk in sectors.