Nested LXD on Ubuntu 16.04.2 (Xenial)

Edit – 1 Jun 2017: The issue is a problematic patch that caused a breakage between 2.0.9 and 2.13. LXD 2.0.10 is currently in the SRU review queue, and once it lands in xenial-updates the problem should go away. tl;dr: Nested LXD containers on Ubuntu 16.04.2 (Xenial) will break if you’re running LXD 2.12+ on the host machine, because the Xenial cloud image ships with LXD 2.0.9 and a version conflict between host and container causes nesting to fail.