use pg_hba instead of ::postgresql::hba in puppetdb::database::postgresql

Note:

- postgresql::hba doesn't work on RHEL so I decided to use the new pg_hba augeas provider
- allow local access to puppetdb database to puppetdb user via unix socket was not enough (postgresql::user needs md5 access to template1 via local TCP socket).
- ugly hack required because we can't get $::postgresql::pg_hba_conf_path from puppetdb::database::postgresql