Major Description
jclouds restricts AMI owners to Amazon, Alestic, Canonical, and Rightscale to avoid slow image ID listings. This can be changed (to pick up your own AMIs) by setting jclouds.ec2.ami-owners to a comma-separated list of owner IDs.
ComputeServiceContextBuilder needs to construct a ComputeServiceContext which passes a properties file with this property from the Whirr configuration. In fact, it should probably pass all properties that start with "jclouds." to ComputeServiceContextBuilder.