JCLOUDS-602 - Add support for volumeType, iops and encrypted to EC2 volumes

Note - still missing adding these to the createVolume* methods, but
that's going to involve a non-trivial change to something like
CreateVolumeOptions.class rather than the current simple arguments.
aside: consider auto-value to write this class, including its tostring etc :)

https://github.com/google/auto/tree/master/value