Changed modules from 'action' to 'postgresql_db' and 'postgresql_user', ...

...introduced into Ansible as of version 0.6. Also changed parameter 'user' to 'name' as specified in the current documentation.

Hello. This is actually my first Github pull request, and my first ansible-examples pull request. I just updated the module name in postgres.yml to match the current docs (http://www.ansibleworks.com/docs/modules.html#postgresql-db). Feel free to let me know how else I can help. ~Steve