init-install: Add a second prompt to install

This also makes it clear that the user will be overwriting
the entire disk.

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>
init-install-efi.sh: Switch to using UUIDs

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>
init-install.sh: Switch to using UUIDs

Signed-off-by: Drew Moseley <drew_moseley@mentor.com>