Use CSS selectors rather than XPath here

Signed-off-by: Michal Čihař <michal@cihar.com>
Pass parameters individually and avoid parsing

Signed-off-by: Michal Čihař <michal@cihar.com>
Use selectors based on form name rather than index

Signed-off-by: Michal Čihař <michal@cihar.com>
Another test which relies on superuser

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