Handle build timeouts, make timeout configurable per app

lib/ember-cli/app.rb

@@ -40,19 +40,46 @@ def wait
       Timeout.timeout(build_timeout) do
         sleep 0.1 while lockfile.exist?
       end
-    end
+    rescue Timeout::Error
+      suggested_timeout = build_timeout + 5
 
-    private
+      warn <<-MSG.strip_heredoc
+        ============================= WARNING! =============================
 
-    def lockfile
-      app_path.join("tmp", "build.lock")
+          Seems like Ember #{name} application takes more than #{build_timeout}
+          seconds to compile.
+
+          To prevent race conditions consider adjusting build timeout
+          configuration in your ember initializer:
+
+            EmberCLI.configure do |config|
+              config.build_timeout = #{suggested_timeout} # in seconds
+            end
+
+          Alternatively, you can set build timeout per application like this:
+
+            EmberCLI.configure do |config|
+              config.app :#{name}, build_timeout: #{suggested_timeout}
+            end
+
+        ============================= WARNING! =============================
+      MSG
     end
 
+    private
+
     delegate :ember_path, to: :configuration
-    delegate :build_timeout, to: :configuration
     delegate :tee_path, to: :configuration
     delegate :configuration, to: :EmberCLI
 
+    def build_timeout
+      options.fetch(:build_timeout){ configuration.build_timeout }
+    end
+
+    def lockfile
+      app_path.join("tmp", "build.lock")
+    end
+
     def prepare
       @prepared ||= begin
         check_addon!