LU-8006 ptlrpc: cleanup codes of TBF command

LU-8006 ptlrpc: cleanup codes of TBF command

The codes of parsing TBF command are improved so as to make it
easier to add new commands. And command format has been changed
to:
For NRS "tbf nid" policy:
lctl set_param ost.OSS.ost_io.nrs_tbf_rule=
	"start $RULE_NAME nid={$NID} rate=$RATE"
For NRS "tbf jobid" policy:
lctl set_param ost.OSS.ost_io.nrs_tbf_rule=
	"start $RULE_NAME jobid={$JOBID} rate=$RATE"

lctl set_param ost.OSS.ost_io.nrs_tbf_rule=
	"change $RULE_NAME rate=$RATE"

Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: Id9861f4c3d894bea614288089622c11124e7f4de
Reviewed-on: http://review.whamcloud.com/19499
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>