Add close_select2 method to select2_helper

**Why?**
This is needed to create a feature test for:
https://gitlab.com/gitlab-org/gitlab-ee/issues/11194

spec/support/helpers/select2_helper.rb

@@ -35,6 +35,10 @@ module Select2Helper
     execute_script("$('#{selector}').select2('open');")
   end
 
+  def close_select2(selector)
+    execute_script("$('#{selector}').select2('close');")
+  end
+
   def scroll_select2_to_bottom(selector)
     evaluate_script "$('#{selector}').scrollTop($('#{selector}')[0].scrollHeight); $('#{selector}');"
   end