Run Selenium tests against MySQL

Signed-off-by: Michal Čihař <michal@cihar.com>
Re-enable Opera testing

Signed-off-by: Michal Čihař <michal@cihar.com>
Disable HttpOnly cookies for testing

Selenium can not clear HttpOnly cookies in MSIE, see
https://code.google.com/p/selenium/issues/detail?id=5101

Signed-off-by: Michal Čihař <michal@cihar.com>