I installed sheepdog on 2.0 when it was still beta, not sure if anything changed to break it since then.
Here are my notes on how I installed it:
It did work, used lots of CPU and was a little slower than expected.
apt-get install libcorosync-pve-dev git dh-autoreconf pkg-config
git clone git://github.com/collie/sheepdog.git
To get a drive in your VM you need to do something like this in the vmid.conf file where "test1" is the name of a sheepdog image:
args: -drive file=sheepdog:test1,if=none,id=drive-virtio0,cache=none,aio=native -device virtio-blk-pci,drive=drive-virtio0,id=virtio0,bus=pci.0,addr=0xa,bootindex=102