Fix regression in EC2 disk volumeType, removed in merge of GCE branch.
EC2: allow EBS volumes to be encrypted using the EBS encryption feature, where Amazon takes care of the encryption+keys. Default is still using luks encryption.
Fix encrypted disk on GCE. Fixes #235
linode: Add linode support stub
linode: Implement machine creation
linode: some utility methods
linode: configuration creation