LU-14398 hsm: use llapi_fid2path_at() in the copytool

LU-14398 hsm: use llapi_fid2path_at() in the copytool

In lhsmtool_posix.c and liblustreapi_hsm.c, convert several uses of
uses of llapi_fid2path() to llapi_fid2path_at().

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Ice64d02010b4260287be4d4e26c6b75b178bc81b
Reviewed-on: https://review.whamcloud.com/41408
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>