LU-8328 tests: cleanup system after conf-sanity test_86

LU-8328 tests: cleanup system after conf-sanity test_86

The conf-sanity test_86 reformats the OST1 device, it only
checks whether the reformat works or not, but it does not
reformat the MGS (or write conf) as to after reformatting
the OST1, it cannot mount to the MGS, so if the subsequent
tests do not reformat the system, then will get failure.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I808d7d6c3fa2e57e8b644bd4af7350be006605c3
Reviewed-on: http://review.whamcloud.com/20987
Tested-by: Jenkins
Reviewed-by: Emoly Liu <emoly.liu@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>