LU-12932 lod: rename qos_threshold_rr parameter

LU-12932 lod: rename qos_threshold_rr parameter

Rename the qos_thresholdrr parameter back to its original name of
qos_threshold_rr so that there is no interop breakage. Update
test to handle mdt_qos_threshold_rr which lines up with the name
of qos_* sysfs files. Since we are using directly kstrtouint()
we have to eat the '%' that could be passed in.

Change-Id: I318a2ece6910e28a7a2331851d13b2269cf23e28
Fixes: c1d0a355a6a6 ("LU-12624 lod: alloc dir stripes by QoS")
Test-Parameters: trivial testlist=sanityn
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/36686
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>