Optionally publish to Artifactory using the Omnibus publisher

If the release script is called with the `—-publish-to-artifactory` option each artifact will be published to Artifactory in addition to the normal Omnitruck publishing tasks.

Example of publishing result in Artifactory:

![artifactory_standalone-ubuntu-1404____repository_browser](https://cloud.githubusercontent.com/assets/6164/4082714/3755af10-2ef4-11e4-89b5-8c9214a881a3.png)


/cc @opscode/release-engineers @opscode/client-engineers