Upgrade puppet to version 3.5

Opening for discussion - i've had success running with 3.5 on mongo-1 and 
development-1 in vagrant. I'd suggest deploying this branch on preview and
seeing what issues arise, if people are happy with that.

Upgrading to 3.6 didnt seem to work immediately on development-1 - seems it 
might be a quick win to upgrade to 3.5 (assuming things work on preview)