add support for overlayroot (and crypt)

[Kapil Thangavelu]

Cloud-init needs support for enabling and configuring overlayroot (and crypt) so that this can be turned on at instance start.

[Wzrd1 (stephen-p-villano)]

Would this cause an error during an update-grub? I get /usr/sbin/grub-probe: error: failed to get canonical path of `overlayroot' on my test box.
The system boots OK in spite of that and it's running kernel 3.13.0-19-generic now.

[Wzrd1 (stephen-p-villano)]

An update.
I'm unable to update the kernel with overlayroot in place.
update-initramfs: Generating /boot/initrd.img-3.13.0-19-generic
cryptsetup: WARNING: failed to detect canonical device of /media/root-ro/
cryptsetup: WARNING: could not determine root device from /etc/fstab

update-grub
/usr/sbin/grub-probe: error: failed to get canonical path of `overlayroot'.

[James Falcon (falcojr)]

Tracked in Github Issues as https://github.com/canonical/cloud-init/issues/2426