Add set bad lba function in md-faulty module.

["majianpeng" <majianpeng@gmail.com>]

Hi all:
	In order to test md code, sometime we need  simulate read/write harddisk error.
	Using hdparm --make-bad-sector to  simulate  read error.But I did not find way of  simulating write-error.
	I tested md-faulty module, it can do this.But it is not provide the function link hdparm --make-bad-sector,which did not set lba.
	Using hdpamr --make-bad-sector to  simulate read error can cause some problem.
	It will cause ata commnd reset,disk reset and so on.It take too log time.
	So I think add a function in md-faulty which can set read/write lba.
	How about ?
											
 				
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majianpeng
2012-05-15