Allow custom resolver during cache prep

Allows operator override for the DNS resolver to use during the
cache preparation.

Change-Id: I3ca3f4b8cc342928c8e65d87697660ca8a8f5400

defaults/main.yml

@@ -102,6 +102,10 @@ lxc_image_compression_ratio: 0
 #       dest: "/etc/issue"
 lxc_container_cache_files: []
 
+# DNS servers to use during cache preparation
+lxc_cache_prep_dns:
+  - "{{ lxc_net_address }}"
+
 # Custom shell commands to run before/after the LXC cache prep process has taken
 # place.
 lxc_cache_prep_pre_commands: '## pre command skipped ##'

vars/redhat-7.yml

@@ -52,7 +52,9 @@ lxc_cache_map:
     if [ -a /etc/resolv.conf ]; then
       mv /etc/resolv.conf /etc/resolv.conf.org
     fi
-    echo "nameserver {{ lxc_net_address }}" > /etc/resolv.conf
+    {% for resolver in lxc_cache_prep_dns %}
+    echo "nameserver {{ resolver }}" >> /etc/resolv.conf
+    {% endfor %}
     yum install -y {{ lxc_cache_distro_packages | join(' ') }}
     rm -f /usr/bin/python
     ln -s /usr/bin/python2.7 /usr/bin/python

vars/ubuntu-16.04.yml

@@ -54,7 +54,9 @@ lxc_cache_map:
     if [ -a /etc/resolv.conf ]; then
       mv /etc/resolv.conf /etc/resolv.conf.org
     fi
-    echo "nameserver {{ lxc_net_address }}" > /etc/resolv.conf
+    {% for resolver in lxc_cache_prep_dns %}
+    echo "nameserver {{ resolver }}" >> /etc/resolv.conf
+    {% endfor %}
     apt-key add /root/repo.keys
     rm /root/repo.keys
     export DEBIAN_FRONTEND=noninteractive