LU-17814 utils: Add work unit management

LU-17814 utils: Add work unit management

Add creating and removing the root work unit.

Still no actual find, but closer.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Id56e43042b6e6ea776fae20b53837c9eced5098e
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57293
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Marc Vef <mvef@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>