Please backport lxd 0.22-0ubuntu2 (main) from xenial

Please backport lxd 0.22-0ubuntu2 (main) from xenial to trusty.

Reason for the backport:
========================
Update to the current version from xenial and fix a security issue.

Testing:
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Mark off items in the checklist [X] as you test them, but please leave the checklist so that backporters can quickly evaluate the state of testing.

You can test-build the backport in your PPA with backportpackage:
$ backportpackage -u ppa:<lp username>/<ppa name> -s xenial -d trusty lxd

* trusty:
[x] Package builds without modification
[x] lxd-client-dbgsym installs cleanly and runs
[x] lxd-tools installs cleanly and runs
[x] lxd-client installs cleanly and runs
[x] lxd installs cleanly and runs
[x] lxd-dbgsym installs cleanly and runs
[x] lxd-tools-dbgsym installs cleanly and runs

No reverse dependencies