configure /etc/default/locale with the LANG value during image generation

[Ryan Harper]

Cloud-images currently include en_US.UTF-8 locales already generated; This has been the default locale for cloud-images for sometime. Please emit the LANG="en_US.UTF-8" value into /etc/default/locale so locales are not regenerated.

The artful image current sets this file. Xenial and Zesty images contain en_US.UTF-8 locales but do not configure /etc/default/locale.

% ls -al *server*
-rw-rw-r-- 1 rharper rharper 318898176 Oct 26 16:01 artful-server-cloudimg-amd64.img
-rw-rw-r-- 1 rharper rharper 291831808 Oct 26 16:01 xenial-server-cloudimg-amd64-disk1.img
-rw-rw-r-- 1 rharper rharper 349831168 Oct 26 16:01 zesty-server-cloudimg-amd64.img

(foudres) tmp % for img in *server*.img; do sudo mount-image-callback $img -- chroot _MOUNTPOINT_ /bin/bash -xc 'cat /etc/os-release; cat /etc/cloud/build.info; cat /etc/default/locale; locale -a'; echo ""; done
+ cat /etc/os-release
NAME="Ubuntu"
VERSION="17.10 (Artful Aardvark)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 17.10"
VERSION_ID="17.10"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=artful
UBUNTU_CODENAME=artful
+ cat /etc/cloud/build.info
build_name: server
serial: 20171025
+ cat /etc/default/locale
LANG=C.UTF-8
+ locale -a
C
C.UTF-8
en_US.utf8
POSIX

+ cat /etc/os-release
NAME="Ubuntu"
VERSION="16.04.3 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.3 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial
+ cat /etc/cloud/build.info
build_name: server
serial: 20171025
+ cat /etc/default/locale
# File generated by update-locale
+ locale -a
C
C.UTF-8
en_US.utf8
POSIX

+ cat /etc/os-release
NAME="Ubuntu"
VERSION="17.04 (Zesty Zapus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 17.04"
VERSION_ID="17.04"
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
VERSION_CODENAME=zesty
UBUNTU_CODENAME=zesty
+ cat /etc/cloud/build.info
build_name: server
serial: 20171026
+ cat /etc/default/locale
# File generated by update-locale
+ locale -a
C
C.UTF-8
en_US.utf8
POSIX