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.
I think I was trying to avoid adding the form field if it wasn't necessary and did it in a kind of ass-backwards way. Will clean up.