Fix failing e2e labels test

On staging new projects now have existing labels, which displays a
different layout causing a test to fail because an expexted image
is not displayed.

There is a similar image shown on the page with existing labels, so
this change adds a selector so the test can successfully wait for the
image to appear.

app/views/shared/empty_states/_priority_labels.html.haml

@@ -1,4 +1,4 @@
 .text-center
-  .svg-content
+  .svg-content.qa-label-svg
     = image_tag 'illustrations/priority_labels.svg'
   %p Star labels to start sorting by priority

qa/qa/page/label/index.rb

@@ -14,6 +14,10 @@ module QA
           element :label_svg
         end
 
+        view 'app/views/shared/empty_states/_priority_labels.html.haml' do
+          element :label_svg
+        end
+
         def go_to_new_label
           # The 'labels.svg' takes a fraction of a second to load after which the "New label" button shifts up a bit
           # This can cause webdriver to miss the hit so we wait for the svg to load (implicitly with has_element?)