Add unit tests for convertToRelativePath
Refer to relative path instead of absolute path

There is no need to refer to the absolute path here if we can use the relative one.

Conflicts:
	lib/private/templatelayout.php

Conflicts:
	lib/private/templatelayout.php
Add "$_SERVER['REQUEST_URI']" to fix the unit tests

Let's hope that works
Add proper setup and teardown

Properly restore REQUEST_URI and SCRIPT_NAME after test runs
Merge pull request #11673 from owncloud/backport-11593

Backport #11593