generic/317: Use relative paths to avoid traversal permission problems

generic/317: Use relative paths to avoid traversal permission problems

generic/317 will fail because execvp(cmd) is executed without permission,
where cmd is '$here/src/lstat64 $file', which is called by
  $here/src/nsexec -s -U -M "0 $qa_user_id 1000" -G "0 $qa_user_id 1000"\
  $here/src/lstat64 $file

So, you will see following output:
  From user_ns
  ...
  +execvp: Permission denied

nsexec runs the instruction '$here/src/lstat64 $file' as a regular user,
the regular user may not have permission to access path in '$here'.

Actually, it has been fixed in 4818302fbf ("xfstests: generic/317 use
relative paths..."), which then been modified by b7cecbea22 ("fstests:
Add path $here before src/<file>").

Fixes: b7cecbea22 ("fstests: Add path $here before src/<file>")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>