Fix stubbing of ActiveRecord that doesn't work in AR 3.2.*

These tests worked really hard to try and stub out the AR stack and avoid
using a database - which worked, until the AR 3.2 series changed their
internals and so the stubbing stopped working.

Instead, rewrite the tests to actually use a database. Works much better and
catches way more errors, even if the tests run marginally less often.
Honestly, though, almost everything here is database layer behaviour...

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>