Allow the provisioner to install Ubuntu 12.04

These are the bare minimums to install Ubuntu 12.04 on a non-admin node.
This should be sufficient to enable us to start working on porting over
workload barclamps.
Merge pull request #212 from VictorLowther/pull-req-master-bd66348553d542ca5099c3c0ee4e662fe322da9f

https://github.com/crowbar/barclamp-provisioner/pull/212

Merged by devtool for cloudedge