Fixes #7733 - Remove hosts.yml fixtures and use FactoryGirl instead

Ok, this is huge, Apologies to whoever ens up having to review this. Fortunately all the changes are in test/ so we know the functionality hasn't changed. I'd like at least two reviews so that we keep confidence in the test coverage - @ares can you do the first one?

There's probably substantial improvements we can make in the Host factory traits, feel free to suggest.
Would this work?
```ruby
@host1, @host2, @host3 = FactoryGirl.create_list(:host, 3,  :location => taxonomies(:location1),
                                :organization => taxonomies(:organization1),
                                :puppetclasses => [puppetclasses(:one)],
                                :environment => environments(:production))
```