Implementation of packer builder for Outscale Cloud Provider.

The point of this request is to add a new cloud provider to the list of supported builders by packer. Outscale (http://www.outscale.us/en/) is a cloud provider which is active since 2011, have a worldwide presence and handles hundreds of thousands of vm instances on a daily basis. 

The main aspect that makes outscale different from the other cloud providers is that the public API it offers is largely compatible with amazon EC2. Although the behavioural differences between Outscale and AWS EC2 require special modifications of the amazon-* builders ( except amazon-instance which cannot be adapted because Outscale lacks an S3 compatible service for the moment).

If you need more information about this pull request and want to talk about it directly, you can contact me on IRC freenode network, nickname WintermeW.

Best Regards,
Clément Gamé
R&D Cloud Engineer
Outscale SAS.