LU-16814 utils: Change llapi_root_path_open() signature

LU-16814 utils: Change llapi_root_path_open() signature

This patch changes llapi_root_path_open() first argument
form char * to const char * as the argument passed is
not modified.

This patch also fixes llapi_rmfid and llapi_root_path_open
man page.

Fixes: 5d93025240 ("LU-16427 lfs: rmfid does not print anything on error")
Reported-by: Thomas Bertschinger <bertschinger@lanl.gov>
Test-Parameters: trivial testlist=sanity
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I81de8cb9280af91af8a2de8dbb51f8e82807220d
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50909
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Thomas Bertschinger <bertschinger@lanl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>