Actually run `apt-get update` if required

Fixes the fix in 602ba7a71d647b97cb8c0f7e9fe0d6913ac7a255
Tweak postgresql test
Update to Ruby 2.1
driver_config -> driver
ruby-switch is no longer required

and it is removed in Ubuntu 14.04 LTS anyway
Use new Vagrant box: Ubuntu Server 14.04 LTS from Canonical

https://vagrantcloud.com/ubuntu/trusty64
Give VM more CPU & RAM
Use version of postgresql cookbook that supports Ubuntu 14.04
Let Test-Kitchen test against Ubuntu 14.04
Adapt postgresql test