Comment 0 for bug 1689557

Blake and I did some work to test out usage or rooturl.
The general goal was to drop usage of iscsi root for enlistment,
commissioning, deployment and rescue.

The package that enables this is cloud-initramfs-rooturl [1], part of
cloud-initramfs-tools source package.

In order to accomplish this, what needs to be done are
A. changes in maas to send kernel parameters with 'rooturl=' wherever
   it previously used iscsi_* and change root= to be of the format:
       root=squashfs:http://url/...

B. changes in maas to remove usage and management of tgt. This should
   include at some point completely removing the tgt items found in
   an upgrade to clean disk space.

C. changes in maas-images to build squashfs images for supported releases.
   Currently maas-images (v3) only builds squashfs for xenial+. We will
   at minimum need trusty, and likely need precise.

   Another path to this would be to have maas send the rooturl=...tar.xz
   However, having consistently for all releases would be good.

Under bug 1688606:
D. SRU of cloud-initramfs-rooturl to trusty, xenial, yakkety and
   possibly precise.
E. maas-images modification to include cloud-initramfs-rooturl in
   the packages that are built in the initramfs (note, that does not
   need to change the image itself, only the kernel/initrd packs:
   kpack-from-image).

Related bugs:
 * bug 1688606: SRU cloud-initramfs-rooturl to archive