core, restapi, webadmin, userportal: cloud-init [3/6] - backend

Support using cloud-init to perform initial setup of virtual machines.

Further details available at:
http://www.ovirt.org/Features/Cloud-Init_Integration

This patch adds backend support to generate cloud-init configuration
payload from a CloudInitParameters object that can accompany a Run VM
request.

Changes to rest api, webadmin, and userportal are minimal and only for
compatibility with backend changes.

Change-Id: Ida8ffa5b92ff79cdac5e401c0a815ffcf517590d
Signed-off-by: Greg Padgett <gpadgett@redhat.com>