Update lxd dependency

[babbageclunk]

This includes lxc/lxd#2480 which fixes a goroutine leak (actually 2 goroutines) anywhere we create a LXD client.

Part of http://pad.lv/1625774

QA steps:

• bootstrap a LXD controller

• monitor the number of goroutines running in the controller agent

  I use:

#!/bin/bash
juju ssh -m controller 0 "sudo apt install socat;
(socat tcp-listen:8080,reuseaddr,fork abstract-connect:jujud-machine-0) &
sleep 1
watch '(curl localhost:8080/debug/pprof/goroutine?debug=2 2> /dev/null) | grep \"^goroutine\" | wc -l'"

• add a model, note goroutine increase
• destroy the model, goroutines should go back to same level as before

Before the update, there would be 10 more goroutines for each add/destroy (read- and write-loops for 5 idle keep-alive connections).

[macgreagoir]

(IANAGR) LGTM, checked sha and timestamp in lxc/lxd repo.

[frobware]

I previously ran into build issues when bumping the lxd dependencies - mgz has the detail.

I would double-check that they can still build the debs with this change.

[babbageclunk]

I checked with balloons, he says it should be ok.

$$merge$$

[jujubot]

Status: merge request accepted. Url: http://juju-ci.vapour.ws:8080/job/github-merge-juju