LU-17699 utils: new --skip option for lfs find

LU-17699 utils: new --skip option for lfs find

Added [--skip | -k] options for 'lfs find' to skip a percentage of all
files. This brings the benifit of allowing a certain percentage of the
files in the scanned directory to be migraated to new OSTs instead of
migrating entire directory trees. Note that the file size is not taken
into account when skipping files which could result in an unbalanced
set of files being returned. If there are fewer than 25 files there
could be an increased margin of error with the results, however it
should still be relatively negligable (at most 10%).

Planned to implement further utility with --skip-rebalance which would
calculate the pertentage of files that needed to be return vs. skipped
based on the fullness ratio of each OST vs. the avergae fullness of a
balanced filesystem to avoid the user having to calculate the skip
percentage themselves.

Signed-off-by: Frederick Dilger <fdilger@whamcloud.com>
Change-Id: I3ff1600f25f3be54f2a353fa78f7b8b7f98f591a
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55200
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>