LU-4724 hsm: Safe copytool event logging

LU-4724 hsm: Safe copytool event logging

Protect against concurrent event log writes by multiple
threads within a copytool process. Fixes sanity-hsm test_71
failures.

Signed-off-by: Michael MacDonald <michael.macdonald@intel.com>
Change-Id: Ie18f7368f386acf0949a038e6bdb2ba7dca5c3a3
Reviewed-on: http://review.whamcloud.com/9553
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>