[WIP] Travis CI bundle cache

Trying to see how much a bundle cache will speed up the travis tests.

This PR uses the s3-put script as found here: http://mislav.uniqpath.com/2013/12/travis-cached-bundle/
could you change all of these to:
```
task :brakeman => %w(test:set_env test:load_vmdb_tasks brakeman:run)
```

you'd need to write task `test` that sets `ENV['RAILS_ENV'] = 'test'`

and maybe one that has: `'test:upload_s3_bundle_cache' if upload_s3_bundle_cache?`