Move lxc_cache_distro_packages to defaults

Move the package list from vars/ to defaults/ to allow for overriding
in inventory group/host vars.

Change-Id: Idb186a061a396713a0e449d47ec262b30d5006ca

defaults/main.yml

@@ -125,6 +125,9 @@ lxc_cache_prep_dns:
 lxc_cache_prep_pre_commands: '## pre command skipped ##'
 lxc_cache_prep_post_commands: '## post command skipped ##'
 
+# List of packages to be installed into the base container cache
+lxc_cache_distro_packages: "{{ _lxc_cache_distro_packages }}"
+
 # Set the servers to download LXC images from
 # NOTE(mhayden): The main images.linuxcontainers.org site will redirect
 # requests to (us|uk).images.linuxcontainers.org upon the first request. We

releasenotes/notes/cache-packages-override-e89847687abddf34.yaml

@@ -0,0 +1,4 @@
+---
+features:
+  - The ``lxc_cache_distro_packages`` has been moved to the role defaults from vars to enable
+    easier overriding of the container cache package list.

vars/redhat-7.yml

@@ -79,7 +79,7 @@ lxc_cache_map:
     fi
     {{ lxc_cache_prep_post_commands }}
 
-lxc_cache_distro_packages:
+_lxc_cache_distro_packages:
   - ca-certificates
   - cronie
   - epel-release

vars/suse-42.yml

@@ -84,7 +84,7 @@ lxc_cache_map:
     systemctl -q enable sshd
     {{ lxc_cache_prep_post_commands }}
 
-lxc_cache_distro_packages:
+_lxc_cache_distro_packages:
   - ca-certificates
   - ca-certificates-mozilla
   - git-core

vars/ubuntu-16.04.yml

@@ -99,7 +99,7 @@ lxc_cache_map:
 # ref: http://serverfault.com/questions/259226/automatically-keep-current-version-of-config-files-when-apt-get-install
 lxc_cache_install_debconf: '-o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" --force-yes'
 
-lxc_cache_distro_packages:
+_lxc_cache_distro_packages:
   - apt-transport-https
   - build-essential
   - ca-certificates