Milestone ProvisioningService: Support for GENI slice management

Add support for GENI slice management.

Stork now supports slice management in two ways. First, we have demonstrated using Stork with Gush to deploy the software needed for a Gush experiment. See ​http://raven.cs.arizona.edu/projects/project/wiki/StorkForGush for details. Second, we have created an augmented version of the SFI tool that integrates support for uploading packages to the Stork repository. This allows a user who is already familiar with SFI to seamlessly upload packages to Stork without needing to use a different tool.