Hacky method, but in welcome controller, use subprocess to
call a script which invokes curtin at a known location with
a specific set of parameters.
Modify the installer configuration and start-up scripts to
ensure Subiquity runs on tty1 and keeps the service running.
Upon hitting 'Confirm' Subiquity will exec curtin_wrap.sh
which calls the *real* curtin. Cloud-init user-data has been
modified to unpack the curtin archive embedded.
When complete, the target.img file is bootable.
Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
Adam Stokes