LU-16768 lfs: copy optarg string other than using it directly

LU-16768 lfs: copy optarg string other than using it directly

Copy optarg string for fp_format_printf_str lest it be messed
later.

Lustre-change: https://review.whamcloud.com/50733
Lustre-commit: 75db98cef3df8f9a0e1b6e7a5150f3c332e6167b

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: Ib32883d3261ae921adf0fdd7b05bcbf728de7557
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/50690
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>