support dockerfiles without expose command. closes #1083

tests/apps/dockerfile-noexpose/CHECKS

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+/ Hello World!

tests/apps/dockerfile-noexpose/Dockerfile

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+FROM ubuntu:trusty
+ENV LC_ALL C
+ENV DEBIAN_FRONTEND noninteractive
+ENV DEBCONF_NONINTERACTIVE_SEEN true
+
+RUN apt-get install -y software-properties-common && add-apt-repository ppa:chris-lea/node.js && apt-get update
+RUN apt-get install -y build-essential curl postgresql-client-9.3 nodejs git
+
+COPY . /app
+WORKDIR /app
+RUN npm install
+
+CMD npm start

tests/apps/dockerfile-noexpose/check_deploy

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+#!/usr/bin/env bash
+set -e; output="$(curl -s -S $1)"; echo $output; test "$output" == "Hello World!"

tests/apps/dockerfile-noexpose/index.js

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+var express = require('express')
+var app = express();
+
+app.set('port', (process.env.PORT || 5000))
+app.use(express.static(__dirname + '/public'))
+
+app.get('/', function(request, response) {
+  response.send('Hello World!')
+})
+
+app.listen(app.get('port'), function() {
+  console.log("Node app is running at localhost:" + app.get('port'))
+})

tests/apps/dockerfile-noexpose/package.json

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+{
+  "name": "node-js-sample",
+  "version": "0.1.0",
+  "description": "A sample Node.js app using Express 4",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js"
+  },
+  "dependencies": {
+    "express": "^4.0.0"
+  },
+  "engines": {
+    "node": "0.10.x"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/heroku/node-js-sample"
+  },
+  "keywords": [
+    "node",
+    "heroku",
+    "express"
+  ],
+  "author": "Mark Pundsack",
+  "contributors": [
+    "Zeke Sikelianos <zeke@sikelianos.com> (http://zeke.sikelianos.com)"
+  ],
+  "license": "MIT"
+}