Adjust acceptance tests to notifications based on toastify

The old notifications were added as ".row" elements to the
"#notification-container" element; the new notifications based on
toastify are added as ".toastify .on .toast..." elements to the
"#content" element. Besides that, they also include a span element with
an X to close the notification, so now only the first child text node
should be compared to the expected message.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>