LU-5830 scripts: use lustre_rmmod in lnet start/stop script

LU-5830 scripts: use lustre_rmmod in lnet start/stop script

In lnet's start/stop script stop phase, use lustre_rmmod instead
to try to unload a static list/sequence of modules.

This patch is back-ported from the following one:
Lustre-commit: f882ceaa28d5c0fb2f018102468656d9b7adc637
Lustre-change: http://review.whamcloud.com/12513

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ida7093e10b198c73a4cd8ca539f4b803dd998e00
Reviewed-on: http://review.whamcloud.com/12587
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>