LU-2744 build: fix race issues thanks to oap_lock

LU-2744 build: fix race issues thanks to oap_lock

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.

This patch is dedicated to code fragments involving oap_lock.

Signed-off-by: Sebastien Buisson <sebastien.buisson@bull.net>
Change-Id: Ibfd5fe6338c624a1ab98b83ec621bcd88d736491
Reviewed-on: http://review.whamcloud.com/6572
Tested-by: Hudson
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>