Add new ubuntu-upstart image specifically to make it really easy to run "machine mode" containers based on upstart/ubuntu

```console
$ ./stackbrew/brew-cli -n tianon -b ubuntu-upstart --targets ubuntu-upstart git://github.com/tianon/stackbrew
2014-01-23 09:43:05,086 INFO Cloning docker repo from git://github.com/tianon/stackbrew, branch: ubuntu-upstart
2014-01-23 09:43:06,348 INFO [cache miss] 8b48f34750cd5185bec7fcbc46a12f38
2014-01-23 09:43:06,348 INFO Cloning git://github.com/tianon/dockerfiles (ref: 47583c4bb2e8db0a42f3f23f3fe54666a2d8606b)
2014-01-23 09:43:07,067 INFO Building using dockerfile...
2014-01-23 09:44:01,084 INFO Committing to tianon/ubuntu-upstart:latest
2014-01-23 09:44:01,086 INFO Registering as processed: 8b48f34750cd5185bec7fcbc46a12f38
2014-01-23 09:44:01,611 INFO [cache hit] 8b48f34750cd5185bec7fcbc46a12f38
2014-01-23 09:44:01,612 INFO This ref has already been built, reusing image ID
2014-01-23 09:44:01,612 INFO Committing to tianon/ubuntu-upstart:precise
2014-01-23 09:44:01,614 INFO Registering as processed: 8b48f34750cd5185bec7fcbc46a12f38
2014-01-23 09:44:02,159 INFO [cache hit] 8b48f34750cd5185bec7fcbc46a12f38
2014-01-23 09:44:02,159 INFO This ref has already been built, reusing image ID
2014-01-23 09:44:02,159 INFO Committing to tianon/ubuntu-upstart:12.04
2014-01-23 09:44:02,161 INFO Registering as processed: 8b48f34750cd5185bec7fcbc46a12f38
2014-01-23 09:44:02,702 INFO [cache miss] 85a34143616da44e979b84e62bfb7441
2014-01-23 09:44:02,702 INFO Cloning git://github.com/tianon/dockerfiles (ref: 47583c4bb2e8db0a42f3f23f3fe54666a2d8606b)
2014-01-23 09:44:02,909 INFO Building using dockerfile...
2014-01-23 09:47:59,332 INFO Committing to tianon/ubuntu-upstart:quantal
2014-01-23 09:47:59,334 INFO Registering as processed: 85a34143616da44e979b84e62bfb7441
2014-01-23 09:47:59,950 INFO [cache hit] 85a34143616da44e979b84e62bfb7441
2014-01-23 09:47:59,950 INFO This ref has already been built, reusing image ID
2014-01-23 09:47:59,950 INFO Committing to tianon/ubuntu-upstart:12.10
2014-01-23 09:47:59,952 INFO Registering as processed: 85a34143616da44e979b84e62bfb7441
2014-01-23 09:48:00,491 INFO [cache miss] b6afb3d2b3653cab6578a37140822886
2014-01-23 09:48:00,491 INFO Cloning git://github.com/tianon/dockerfiles (ref: 47583c4bb2e8db0a42f3f23f3fe54666a2d8606b)
2014-01-23 09:48:00,705 INFO Building using dockerfile...
2014-01-23 09:52:46,455 INFO Committing to tianon/ubuntu-upstart:raring
2014-01-23 09:52:46,457 INFO Registering as processed: b6afb3d2b3653cab6578a37140822886
2014-01-23 09:52:46,999 INFO [cache hit] b6afb3d2b3653cab6578a37140822886
2014-01-23 09:52:46,999 INFO This ref has already been built, reusing image ID
2014-01-23 09:52:46,999 INFO Committing to tianon/ubuntu-upstart:13.04
2014-01-23 09:52:47,001 INFO Registering as processed: b6afb3d2b3653cab6578a37140822886
2014-01-23 09:52:47,487 INFO [cache miss] 2ddc835c7779f2fb944935054ec89ce6
2014-01-23 09:52:47,488 INFO Cloning git://github.com/tianon/dockerfiles (ref: 47583c4bb2e8db0a42f3f23f3fe54666a2d8606b)
2014-01-23 09:52:47,702 INFO Building using dockerfile...
2014-01-23 09:57:53,512 INFO Committing to tianon/ubuntu-upstart:saucy
2014-01-23 09:57:53,514 INFO Registering as processed: 2ddc835c7779f2fb944935054ec89ce6
2014-01-23 09:57:54,930 INFO [cache hit] 2ddc835c7779f2fb944935054ec89ce6
2014-01-23 09:57:54,930 INFO This ref has already been built, reusing image ID
2014-01-23 09:57:54,930 INFO Committing to tianon/ubuntu-upstart:13.10
2014-01-23 09:57:54,932 INFO Registering as processed: 2ddc835c7779f2fb944935054ec89ce6
2014-01-23 09:57:54,934 INFO BREW BUILD SUMMARY
-------------------------------------------------------------
OVERALL SUCCESS: True
-------------------------------------------------------------
ubuntu-upstart
-------------------------------------------------------------
21 | OK | 4f3b37562590                                      
22 | OK | 4f3b37562590                                      
 6 | OK | 70754f6a4131                                      
26 | OK | 358c9f3bcf0d                                      
17 | OK | 03453b150656                                      
 5 | OK | 70754f6a4131                                      
18 | OK | 03453b150656                                      
25 | OK | 358c9f3bcf0d                                      
 7 | OK | 70754f6a4131                                      
-------------------------------------------------------------
```