LU-13482 utils: bandwidth limit for lfs migrate

LU-13482 utils: bandwidth limit for lfs migrate

Add an option -W to control how much bandwidth
an lfs migrate job can consume. The migrate job
will periodically sleep to meet the bandwidth
restrictions.

This patch also adds a --stats option. The option
produces regular logs entries tracking the progress
of the migrate job. The logs are output in YAML
format. The frequency of the logs is controlled
by --stats-interval. This interval defaults to 5
seconds.

Also included are two tests, 56xh and 56xi. The
first verifies the functionality of the bandwidth
control. The second checks that the output is in
valid YAML and that the stats get printed without
using -W.

Lustre-change: https://review.whamcloud.com/49620
Lustre-commit: 55968bfabe351ad37ee810bf69748ffa56d28037

Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ic71cceb2434a737e3ad8bd325f719e37a70b0047
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49924
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>