OS-2325 Revert imgadm changes exacerbatting this bug

'imgadm import ...' would frequently (always?) hang before this.

This reverts:
* c64ef5b - OS-2315 imgadm fails on images.joyent.com wit
* 0023a4e - IMGAPI-95: imgadm create & imgadm publish (for non-KVM images and VMs)