This appears to be happening again on juju-core 1.18.1. When I attempted to create a new lxc container on the bootstrapped node (machine: 0), I received a lxc-start error. After reviewing this bug report, I manually added in the br0 interface into /etc/network/interfaces and ran ifup br0. Following that, I was able to successfully add a lxc container to machine 0.
This appears to be happening again on juju-core 1.18.1. When I attempted to create a new lxc container on the bootstrapped node (machine: 0), I received a lxc-start error. After reviewing this bug report, I manually added in the br0 interface into /etc/network/ interfaces and ran ifup br0. Following that, I was able to successfully add a lxc container to machine 0.