Merging master into lxd-18.04 branch

[ghatwala]

Able build lxd backend image successfully

# packer build -debug -on-error=abort -only=lxd  <(bin/yml2json < ci-ubuntu-18.04-slim.yml ) > lxd_image_logs_master

# tail -f lxd_image_logs_master
==> lxd: Created image: 8966154aece15b35c8fd5b6014c299152e1ceea60f43ce2aaaccd13b0284fdcd
==> lxd: Unregistering and deleting deleting container...
==> lxd: Running post-processor: shell-local
==> lxd (shell-local): Running local shell script: bin/write-latest-image-name
    lxd (shell-local): time=2019-08-27T10:48:50Z outfile=/root/forked_repo/packer-templates/tmp/ci-ubuntu/latest-image-name template=ci-ubuntu latest_image_name=travis-ci-ubuntu-18
Build 'lxd' finished.
==> Builds finished. The artifacts of successful builds are:
--> lxd: image: 8966154aece15b35c8fd5b6014c299152e1ceea60f43ce2aaaccd13b0284fdcd
--> lxd:
# lxc image list
+---------------------------------+--------------+--------+-------------------------------------------------+---------+-----------+-------------------------------+
|              ALIAS              | FINGERPRINT  | PUBLIC |                   DESCRIPTION                   |  ARCH   |   SIZE    |          UPLOAD DATE          |
+---------------------------------+--------------+--------+-------------------------------------------------+---------+-----------+-------------------------------+

| ubuntu-18.04-slim-latest-master | 8966154aece1 | no     |                                                 | ppc64le | 1028.93MB | Aug 27, 2019 at 10:48am (UTC) |
+---------------------------------+--------------+--------+-------------------------------------------------+---------+-----------+-------------------------------+

@joshk - Any review comments ?