Fix PostgreSQL ossp-uuid extension issues

@jamesc discovered the latest nightly builds of CS12 are causing the Analytics tests to fail with:

```
STDERR: ERROR:  could not open extension control file "/opt/opscode/embedded/share/postgresql/extension/uuid-ossp.control": No such file or directory
---- End output of psql --dbname actions --single-transaction --set ON_ERROR_STOP=1 --command 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"' ----
Ran psql --dbname actions --single-transaction --set ON_ERROR_STOP=1 --command 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp"' returned 1
[2014-12-14T09:53:04+00:00] FATAL: Chef::Exceptions::ChildConvergeError: Chef run process exited unsuccessfully (exit code 1)
```

After some digging it was discovered CS12's PostgreSQL installation was to blame. The latest nightly builds were building two copies of PostgreSQL (9.2.8 and 9.2.9) as some software definitions depended on `postgresql92` and others depended on `postgresql`. There was a time in the past when we shipped two copies of PostgreSQL for upgrade purposes but this is no longer the case with CS12+. This PR finally updates opscode-omnibus to properly depend on the upstream `postgresql` software definitions from omnibus-software.

__PLEASE NOTE__ - Commit a48c538 will be finalized once opscode/omnibus-software#347 is merged.

/cc @opscode/release-engineers @opscode/server-team @jamesc @metadave