Comment 39 for bug 1651602

To verify this is fixed, I have done the following.
For good measure, I've also successfully booted the above
with additional parameter '-smp cpus=2'. That verifies that there is no
obvious regression on SMP system.

$ img_url="http://cloud-images.ubuntu.com/daily/server/xenial/current/xenial-server-cloudimg-amd64-disk1.img"
$ wget "${img_url}" -O disk.img

# patch the image to have a root passwd and disable cloud-init for simplicity.
$ sudo mount-image-callback disk.img -- chroot _MOUNTPOINT_ sh -exc '
    touch /etc/cloud/cloud-init.disabled
    echo "root:root" | chpasswd'

# attached 'get-kernels' enables proposed, installs linux-virtual into disk.img
# and copies kernels out to out.d
$ ./get-kernels disk.img linux-virtual out.d
$ for i in out.d/*info; do echo == $i ==; cat $i; done
== out.d/build.info ==
build_name: server
serial: 20170106.1
== out.d/vmlinuz-4.4.0-57-generic.pkg-info ==
linux-image-4.4.0-57-generic: /boot/vmlinuz-4.4.0-57-generic
== out.d/vmlinuz-4.4.0-59-generic.pkg-info ==
linux-image-4.4.0-59-generic: /boot/vmlinuz-4.4.0-59-generic

$ kver=4.4.0-57 ; qemu-system-x86_64 -enable-kvm -m 512 \
   -drive file=disk.img,if=none,format=qcow2,id=nvme0 \
   -device nvme,drive=nvme0,serial=nvme-0 \
   -snapshot -nographic -echr 0x05 \
   -kernel out.d/vmlinuz-$kver-generic \
   -initrd out.d/initrd.img-$kver-generic \
   -append "root=LABEL=cloudimg-rootfs console=ttyS0"

# if you set 'ver' to 4.4.0-57 (from released kernel version)
# then you see failure to find root device from the initramfs
# if you set 'ver' to 4.4.0-59 (from -proposed) then it finds root,
# and you can log in as root on console with 'root'.