LU-4243 mgs: use proper uuid in mgs_write_log_failnids()

This patch revert the changes to mgs_write_log_failnids() in the
commit d9d27cad, which introduced a regression of that when multiple
'--servicenode' or '--failnode' option specified, the uuid from
first option will be wrongly used for all other connections.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: Ibd989de67fe6851cc75569be3f64dadaec5e6f8c
Reviewed-on: http://review.whamcloud.com/8372
Tested-by: Jenkins
Reviewed-by: Erich Focht <efocht@gmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>