Tests: Autocomplete tests don't actually work without JavaScript

This was masked by the fact they used an "I should find..." step in generic_steps.rb which always returned true. 

Removing that step also uncovered a little can of worms of other tests which had adopted the "I should find..." step on the assumption that it did something different than "I should see..." and therefore appeared to be passing despite casing errors.

In summary, this pull request removes the broken steps, disables the autocomplete tests, and adds a couple of new steps for tests involving attribute values on `img` or `input` tags.