Initialize milestone title if none is provided

This way, if the title is not relevant in the test, we save at
least one line of code.

qa/qa/ee/resource/project_milestone.rb

@@ -16,6 +16,10 @@ module QA
           end
         end
 
+        def initialize
+          @title = "project-milestone-#{SecureRandom.hex(8)}"
+        end
+
         def resource_web_url(resource)
           super
         rescue ResourceURLMissingError