This will pin the installation of puppetlabs/postgresql to version 2.5.0

Since version 3.0.0 is now released, we want to pin against the old revision
everywhere. We already pin in the Modulefile and unit tests, we just forgot
to do it for the rspec-system tests.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #90 from kbarber/maint/master/pin-system-tests-to-old-postgresql-module

This will pin the installation of puppetlabs/postgresql to version 2.5.0