LU-2744 build: fix 'data race condition' issues

LU-2744 build: fix 'data race condition' issues

Fix 'data race condition' defects found by Coverity version
6.5.0:
Data race condition (MISSING_LOCK)
Accessing variable without holding lock. Elsewhere,
this variable is accessed with lock held.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Change-Id: I29825c47f08a893685a62aeea2e49b315149b3d9
Reviewed-on: http://review.whamcloud.com/6573
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>