Copy private key changes over from cloud_servers branch.

Change-Id: I91b238f06692d16124afd2846537b57b0ed01fbd
Add salt to private key encryption.

Change-Id: I8a53ce9a5d6e561712185c2973dcb7d344a18aea
Merge branch 'dev/resource_private_key' into bp-dev/rackspace-cloud-servers-provider
Add test for private_key.

Change-Id: Ie472e80a0592060a1716e79cd47cb266c5599428