[BUGFIX] GeneralUtilityTest does non use absolute path

Some of the 'link' tests for rmdir do not use absolute paths and
only give desired results if current directory is the document root.

Change-Id: I4a06c1a158175e939e70639627bb8e93e7b773fa
Resolves: #47997
Related: #47459
Releases: 6.2
Reviewed-on: https://review.typo3.org/20558
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn