Postgres now installs in newly provisioned VM (fixes #45)

There were 3 problems which caused breakage:

 *  didn't install the RPM for whatever reason => had to [fork the postgres chef recipe](https://github.com/benilovj/postgresql) and make something happen at compile-time rather than run-time. There's probably a better way to do this...
 *  postgresql92-devel package missing => added to dbfit_test recipe
 *  'pg' gem didn't compile => installing 'pg' gem with additional params within dbfit_test recipe