LU-15942 utils: ofd_access_log_reader exit status

LU-15942 utils: ofd_access_log_reader exit status

If no OSTs are mounted then the ofd module may not be leaded and hence
/dev/lustre-access-log/control may not exist. In
ofd_access_log_reader, if --exit-on-close is used then we should
handle this consistently with the case of no access logs by exiting
with status 0.

Lustre-change: https://review.whamcloud.com/47625
Lustre-commit: 9bf968db56ddbad525dffe6fc4b9fde7d55dbde3

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: I91b059bee8941501f2d207d2a48d1ea5ad40ae99
Reviewed-on: https://review.whamcloud.com/48100
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>