List Available UAI Images in Legacy Mode

A user can list the UAI images available for creating a UAI with a command of the form:

user> cray uas images list

For example:

vers> cray uas images list
default_image = "dtr.dev.cray.com/cray/cray-uai-sles15sp1:latest"
image_list = [ "dtr.dev.cray.com/cray/cray-uai-broker:latest", "dtr.dev.cray.com/cray/cray-uas-sles15:latest", "dtr.dev.cray.com/cray/cray-uai-sles15sp1:latest",]