Make old-run-webkit-tests handle setting the results directory properly.

Make old-run-webkit-tests handle setting the results directory properly.
https://bugs.webkit.org/show_bug.cgi?id=102273
<rdar://problem/11571607>

Reviewed by Timothy Horton.

A call to chdirWebkit in old-run-webkit-tests set the current working directory to the OpenSource folder.
Thus setting --results-directory to OpenSource/layout-test-results would create OpenSource/layout-test-results inside the main OpenSource folder.
This caused many other problems including failure to upload test results and failed future test runs.
The solution is to save the current working directory before calling chdirWebKit and then reconstructing the full path to the results directory
using the saved directory when setting $testResultsDirectory.

* Scripts/old-run-webkit-tests:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@134824 268f45cc-cd09-0410-ab3c-d52691b4dbfc