LU-4556 tests: speed up sanity-lfsck and sanity-scrub tests

LU-4556 tests: speed up sanity-lfsck and sanity-scrub tests

1) drop unnecessary devices reformat.
2) drop unnecessary system stop/re-start.
3) replace 'sleep' with wait_update_facet to avoid idle wait.
4) drop unnecessary "-p" option for some "mkdir" cases.
5) replace "touch" with "createmany -m".
6) other code style changes and cleanup.

Test-Parameters: envdefinitions=SLOW=yes testlist=lfsck-performance
Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I047c63b8793fa843fabe1a69b332c42f2f523f68
Reviewed-on: http://review.whamcloud.com/9704
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>