LU-14179 lfs: avoid lfs find error with long paths

LU-14179 lfs: avoid lfs find error with long paths

Test that files created in a directory having an absolute path length
of up to PATH_MAX-1 are properly found with lfs find. This change
might not cover other very deep directory tree (above PATH_MAX).

Lustre-change: https://review.whamcloud.com/41337
Lustre-commit: a6a76df19db61a2015f4cc78f88060f249c955f2

Signed-off-by: Stephane Thiell <sthiell@stanford.edu>
Change-Id: I44726efd5053c593094587e5c8a4652a3a876641
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/48272
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>