Download ubuntu-cloud tarball before building it

tasks/boxes.rake

@@ -1,9 +1,21 @@
 namespace :boxes do
   namespace :build do
+    IMAGE_ROOT = 'https://cloud-images.ubuntu.com/releases/quantal/release-20130206'
+    IMAGE_NAME = 'ubuntu-12.10-server-cloudimg-amd64-root.tar.gz'
+    def download(source, destination)
+      destination = "#{File.dirname __FILE__}/../#{destination}"
+      if File.exists?(destination)
+        puts 'Skipping box image download'
+      else
+        sh "wget #{source} -O #{destination}"
+      end
+    end
+
     desc 'Packages an Ubuntu cloud image as a Vagrant LXC box'
     task 'ubuntu-cloud' do
       sh 'mkdir -p boxes/output'
-      sh 'cp cache/ubuntu-12.10-server-cloudimg-amd64-root.tar.gz boxes/ubuntu-cloud'
+      download "#{IMAGE_ROOT}/#{IMAGE_NAME}", "boxes/ubuntu-cloud/#{IMAGE_NAME}"
+      sh 'rm -f output/ubuntu-cloud.box'
       sh 'cd boxes/ubuntu-cloud && tar -czf ../output/ubuntu-cloud.box ./*'
     end
   end