LU-5744 obdclass: fix problem of muitple MGTs on same node

LU-5744 obdclass: fix problem of muitple MGTs on same node

When a MGT is mounted on a node which already has an running MGT
it will fail as expected since only one MGS can run on a node.
However, the MGS will be stopped by mistake during this process.
This patch fixes the problem.

Signed-off-by: Li Xi <pkuelelixi@gmail.com>
Change-Id: Ibebf59be3d41849d02801a4ac29fca31dc06c408
Reviewed-on: http://review.whamcloud.com/12301
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>