Fix #1564: Use Procfile for process types in Dockerfile apps

* Document new Procfile feature
* Add and update tests
* Fix a typo in generate_scale_file (ref #1923)

tests/apps/dockerfile-procfile/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "node-example",
+  "version": "0.0.1",
+  "dependencies": {
+    "express": "2.5.x"
+  },
+  "engines": {
+    "node": "4.2.x"
+  },
+  "scripts": {
+    "start": "false"
+  }
+}