LU-7419 llog: lock new llog object creation

LU-7419 llog: lock new llog object creation

Lock the new llog object creation to avoid two
process create the same object at the same time.

Signed-off-by: Di Wang <di.wang@intel.com>
Change-Id: Icdc0eec534ca2f15cd0e195df951416953195346
Reviewed-on: http://review.whamcloud.com/17132
Tested-by: Jenkins
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>