LU-9081 config: don't attach sub logs for LWP

Lustre target processes client log to retrieve MDT NIDs and start
LWPs, it goes the same code path of mgc_process_config() just like
processing the target config log, so that sub clds for security,
nodemap, param & recovery will be attached unnecessarily.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I926ec4f33d3899c73a9c000b3ad0c0e5c102dfde
Reviewed-on: https://review.whamcloud.com/25293
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Hongchao Zhang <hongchao.zhang@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>