LU-16766 obdclass: trim kernel thread names in jobids

LU-16766 obdclass: trim kernel thread names in jobids

When collecting jobstats on operations coming from kernel threads, it
is more useful and reduces the noisiness of the data if the names of
kernel threads are trimmed so that all "kworker/CPU:ID" threads are
collected under "kworker", all "ll_sa_PID" threads under ll_sa, etc.

Signed-off-by: Thomas Bertschinger <bertschinger@lanl.gov>
Change-Id: Icd82a99c1153de0277ea5ed3f4b1d92535809921
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51919
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>