'overlay' union-type is not supported

[Tracnar]

EDIT: I saw this bug report which actually says this is fixed
https://bugs.launchpad.net/ubuntu/+source/schroot/+bug/1398569
but I don't see where the change is supposed to be.
I also saw it's already reported on the debian bug system:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=785136
and git
https://github.com/codelibre-net/schroot/issues/1
It's not very clear which repository is supposed to be the main one, I guess the debian one.

The kernel changed the name of overlayfs to overlay (see https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=ef94b1864d1ed5be54376404bb23d22ed0481feb ) and added the workdir option to the mount options.

The overlay union-type should be added to the allowed list, the 10mount script should be updated to add the workdir option for the overlay union-type, with I suppose a variable CHROOT_UNION_WORKDIR_DIRECTORY and the corresponding schroot configuration option.

Additional info:

Error when running schroot:
schroot --option=union-type=overlay
E: /etc/schroot/chroot.d/click-ubuntu-sdk-15.04-armhf: line 12 [click-ubuntu-sdk-15.04-armhf] union-type: Unknown filesystem union type ‘overlay’

Functions with the check:

lib/schroot/chroot/facet/fsunion.cc-143- void
lib/schroot/chroot/facet/fsunion.cc-144- fsunion::set_union_type (const std::string& type)
lib/schroot/chroot/facet/fsunion.cc-145- {
lib/schroot/chroot/facet/fsunion.cc-146- if (type == "aufs" ||
lib/schroot/chroot/facet/fsunion.cc:147: type == "overlayfs" ||
lib/schroot/chroot/facet/fsunion.cc-148- type == "unionfs" ||
lib/schroot/chroot/facet/fsunion.cc-149- type == "none")
lib/schroot/chroot/facet/fsunion.cc-150- this->union_type = type;
lib/schroot/chroot/facet/fsunion.cc-151- else
lib/schroot/chroot/facet/fsunion.cc-152- throw error(type, FSUNION_TYPE_UNKNOWN);

In the 10mount script:
overlayfs)
                 CHROOT_UNION_MOUNT_OPTIONS="lowerdir=${CHROOT_UNION_UNDERLAY_DIRECTORY},upperdir=${CHROOT_UNION_OVERLAY_DIRECTORY}"

Steps to reproduce:

Try to run a schroot with option union-type=overlay:
schroot --option=union-type=overlay

I found this issue on Archlinux, and I guess it will eventually apply to Ubuntu when the kernel is updated.