Filter by subgroup name before determining if our group has a subgroup

We assumed that the QA sandbox group would continually be wiped and
re-created, and thus never have enough subgroups that the one we just
created during a new run wouldn't appear on the first page.

But we know what they say about assumptions.

qa/qa/page/group/show.rb

@@ -6,7 +6,13 @@ module QA
           click_link name
         end
+        def filter_by_name(name)
+          fill_in 'Filter by name...', with: name
+        end
+
         def has_subgroup?(name)
+          filter_by_name(name)
+
           page.has_link?(name)
         end