Fix postgresql for pp-development

This is down to a parse order issue introduced by renaming the
postgresql module (and therefore making it come after the postgres dev
module). Avoided by allowing the globals we need to override to be
provided by hiera. I have chosen to put these variables in common even
though they only apply to three roles to avoid duplication.
Postgres pg_hba expected a netmask

This can be seen a few lines above in the pg_hba, 'allow access to all
users'.
Merge pull request #562 from alphagov/postgresql-fixes

Postgresql fixes