Add uhwm_wait_output cucumber helper

features/steps/x_steps.rb

@@ -1,10 +1,5 @@
 Then /^it must connect to X display$/ do
-  Timeout.timeout(exit_timeout) do
-    loop do
-      break if assert_partial_output_interactive 'Connected to'
-      sleep 0.1
-    end
-  end
+  uhwm_wait_output 'Connected to'
   expect(`sockstat -u`.lines.grep /\s+ruby.+\s+#{@process.pid}/)
     .not_to be_empty
 end