demo/digitalocean: fix after docker repo change

demo/digitalocean/packer/nomad/packer.json

@@ -15,13 +15,13 @@
     {
       "type": "shell",
       "inline": [
+        "apt-key adv --keyserver hkp://p80.pool.sks-keyservers.net:80 --recv-keys 58118E89F3A912897C070ADBF76221572C52609D",
+        "echo 'deb https://apt.dockerproject.org/repo ubuntu-precise main' > /etc/apt/sources.list.d/docker.list",
         "sudo apt-get -y update",
-        "sudo apt-get -y install unzip",
+        "sudo apt-get -y install unzip docker-engine",
         "curl -o /tmp/nomad.zip -L {{ user `bin_url` }}",
         "sudo unzip -d /usr/local/bin /tmp/nomad.zip",
-        "mkdir -p /usr/local/etc/nomad",
-        "curl -s https://get.docker.com/gpg | sudo apt-key add -",
-        "curl -s https://get.docker.com/ | sudo sh"
+        "mkdir -p /usr/local/etc/nomad"
       ]
     },
     {