[lxc-users] Installing lxd doesn't create bridge lxdbr0?

[Dan Kegel]

On ubuntu 16.04, the commands
   sudo apt install lxd
   sudo apt purge lxd
   ip link list
show that lxd leaves behind bridge lxdbr0 after uninstall, tsk tsk.
A tidy user might well do
   sudo ip link del lxdbr0
to clean up after it.

But alas!  If you do that, *future* installs of lxd break, i.e.
   sudo apt install lxd
   lxc launch ubuntu: demo
fails!
  lxc info --show-log demo shows
            lxc 20160430173001.967 ERROR    lxc_conf -
conf.c:instantiate_veth:2594 - failed to attach 'veth7ME5PJ' to the
bridge 'lxdbr0': Operation not permitted
As mentioned in tych0's post
https://github.com/tych0/tycho.ws/issues/1 that can mean the bridge is
missing.

Sure enough, the command
  sudo ip link add name lxdbr0 type bridge
rescues lxd and lets containers start again.

Why does lxd leave that bridge around after apt purge lxd, and why
doesn't it create it again on a new install?

Man, that had me confused.  Heck, I'm still confused.  lxd does a lot
to hide complexity, but there's a bit of a complexity leak here.