Update Dockerfile, sample role

ubuntu:trusty requires an apt-get update before installing any packages.
Update the sample role to use "become" instead of "sudo", and explictly
install version 4, so that it could install correctly.

Building this Dockerfile will demonstrate bug nodesource#33.

Dockerfile

@@ -2,7 +2,8 @@ FROM ubuntu:trusty
 MAINTAINER Mark Wolfe <mark@wolfe.id.au>
 
 # http://docs.ansible.com/ansible/intro_installation.html#latest-releases-via-apt-ubuntu
-RUN apt-get install software-properties-common -y --force-yes
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update && apt-get install software-properties-common -y --force-yes
 RUN apt-add-repository ppa:ansible/ansible
 RUN apt-get update
 RUN apt-get install ansible -y --force-yes

role.yml

@@ -1,6 +1,8 @@
 ---
 - name: Test the Node.js role
   hosts: all
-  sudo: yes
+  become: yes
   roles:
     - role: "ansible-nodejs-role"
+  vars:
+    nodejs_version: '4'