Download IOS images from Cloud Files to a cloud instance

This pull request adds the ability to download IOS images from Cloud Files.  To do this, I did a fresh copy of the files from gns3-gui/cloud to be able to interact with the Rackspace API within the server code.

I modified the json schema for one of the messages. The GUI can now use the "cloud_path" parameter to tell the server where to look for an IOS image in Cloud Files.

Along with this are smaller fixes to bugs found when trying to launch a device on a cloud server.