Use openshift-install coreos print-stream-json

[cgwalters]

Once openshift/installer#4582 lands, this project needs to be ported off of parsing rhcos.json from the installer git to use the new official public API for this which will be openshift-install coreos print-stream-json.

[karmab]

opened #1213 to address

[travier]

#1213 has been merged. Looks like this one is resolved. Thanks!

[hardys]

/close resolved via #1213