fix(vm_image_util): Don't use the full vagrant OEM on vmware_insecure

Only the key is needed, and currently the vagrant OEM is completely
broken outside of vagrant. This gets vmware_insecure images back into
the state that they were before cloud config came along. :)
Merge pull request #238 from marineam/insecure

fix(vm_image_util): Don't use the full vagrant OEM on vmware_insecure