(MODULES-160) Fix creating and checking role in Postgresql::server::role

A role will not be created when updating puppet if it was not created the first
time without this patch. This is a problem when puppet fails to switch locales
on certain systems. This patch changes the behavior of Postgresql::server::role
similar to logic in Postgresql::server::database.
If you remove the requirement on the `CREATE ROLE` doesn't that mean that the alter role resources could be evaluated before the role is created?