ec2_ami_search: support for SSD and IOPS provisioned EBS images

In ec2_ami_search module, add support for the new SSD-backed EBS (ebs-ssd)
volume as well as images with provisioned IOPS (ebs-io1) that Ubuntu images now support.

For details, see this [mailing list announcement](https://lists.ubuntu.com/archives/ubuntu-cloud-announce/2014-June/000055.html).