update documentation and gradle build to accomidate the updated changes to the ansible script for the virtualbox based environment
diff --git a/build.gradle b/build.gradle
index e82f774..936fe76 100644
--- a/build.gradle
+++ b/build.gradle
@@ -107,6 +107,6 @@
 //       should be modified to do so. This likely means that we need to configure docker on the head node
 //       to access the docker registry on the maasdev virtual box.
 task deployMaas(type: Exec) {
-  commandLine '/usr/bin/ansible-playbook', '-i', '10.100.198.202,', '--skip-tags=switch_support,interface_config', 'dev-head-node.yml'
+  commandLine '/usr/bin/ansible-playbook', '-i', '10.100.198.202,', '--skip-tags=switch_support,interface_config', 'dev-head-node.yml', '--extra-vars=external_iface=eth0' 
 }