LU-957 lfsck: user space tools for LFSCK/scrub

LU-957 lfsck: user space tools for LFSCK/scrub

Control LFSCK/scrub by lctl commands:

1) lfsck_start: start LFSCK/scrub with specified parameters.

2) lfsck_stop: stop LFSCK/scrub on the specified MDT device.

3) The LFSCK/scrub status can be obtained through some special
lproc interface. For example: check OI scrub status by:
lctl get_param -n osd-ldiskfs.*.oi_scrub

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I5828c18453c92162fa0dc211324b69d15ecd9fbc
Reviewed-on: http://review.whamcloud.com/3170
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>