twister: Fix race condition in try_making_symlink

Replaces the check-then-create pattern for symlinks with
opportunistic creation. Instead of checking for existence
before creating the symlink, the code now attempts to
create it directly and gracefully handles the case
where it already exists.

Signed-off-by: Tim Pambor <tim.pambor@codewrights.de>
(cherry picked from commit dff24c8c)