REGRESSION (r143931): set-cookie-on-redirect.html breaks subsequent tests

REGRESSION (r143931): set-cookie-on-redirect.html breaks subsequent tests
https://bugs.webkit.org/show_bug.cgi?id=110844

Patch by Sergio Villar Senin <svillar@igalia.com> on 2013-02-26
Reviewed by Alexey Proskuryakov.

Clean up cookies at the beginning and after finishing the test in
order not to break other tests behavior.

* http/tests/cookies/resources/set-cookie-on-redirect.php: clear cookie before returning.
* http/tests/cookies/set-cookie-on-redirect.html: clear all cookies before starting the test.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@144045 268f45cc-cd09-0410-ab3c-d52691b4dbfc