[BUGFIX] Warning in FAL LocalDriverTest

A subfolder without write permissions makes the tearDown in FAL
LocalDriverTest throw a permission denied warning. This is fixed
by resetting the folder to be writable after gathering result
information in the test case.

Change-Id: I1eb9829b39af7ea67076252385e11701d4be3818
Fixes: #42604
Releases: 6.0
Reviewed-on: http://review.typo3.org/16107
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn