let nodes override operatingsystem from config file

This commit was added so that the puppetmaster can always
be ubunut, even when swift is being tested on rhel.

it allows for the nodes to override operatingsystem.

It also adds code so that the puppetmaster does override
its operatingsystem to always be ubuntu.
Merge pull request #55 from bodepd/more_dev_work

let nodes override operatingsystem from config file