Fix select2 version 4 support to handle grouped options

[Empact]

When options are grouped, their group has the class select2-results__option, and the attribute role=group. Absent this fix, that means selections against grouped fields result in:

Capybara::Ambiguous:
  Ambiguous match, found 2 elements matching visible css ".select2-dropdown li.select2-results__option" with text "TEXT" within #<Capybara::Node::Element tag="body" path="/html/body">

The fix is to exclude the group options on lookup.