Get Postgres working

Probably not ready to be merged yet, because it still refers to an argyle branch that's waiting as a pull request against the real repo.

Changes in salt:
- set locale
- add github's public key to ssh_known_hosts

Change in rapidsms-salt fabfile:
- add db user (idempotently)
- add db (idempotently)
This required some additions to argyle that are pending at https://github.com/mlavin/argyle/pull/13