Major Description
We currently have the ability to provision heterogenous clusters by specifying template/image/hardware for specific roles - i.e., "whirr.templates.role1+role2.image=foo". We don't have anything equivalent for BYON - any node in the BYON pool can get assigned to any role group.
We should add the ability to specify BYON instance IDs for role groups in a similar way to the template/image/hardware properties mentioned above, say, as "whirr.templates.role1+role2.byon-instance-ids=id-1+id-2".