Hi,
The Generic image fails to work in Cloudstack because of the trailing slash issue. This patch is required: http://tmp.nux.ro/Hg4-cloud-init-centos-cloudstack-trailingslash.patch
(I've rebuilt your cloud-init with this patch and I can confirm ssh key authentication works OK)
https://bugs.launchpad.net/cloud-init/+bug/1356855/
But, its able to consume all the other datasources without needing to set priority order. Can you verify this is still the case with cloud-init 0.7.5 and propose a patch against the cloud.cfg file in https://git.centos.org/summary/rpms!cloud-init.git in branch c7-extras ?
Sure, will do. 0.7.4 was not capable of this, which is why I haven't even thought of attempting it. I'll update you with my findings.