Change the logic in `get_openshift_secret_token`

Check for `OPENSHIFT_APP_NAME` and `OPENSHIFT_APP_UUID` only if
there is no `OPENSHIFT_SECRET_TOKEN`.
Improve openshiftlibs to get cloud DB configuration from env variables
Improve settings.openshift DB settings

- Configure PostgreSQL only if it is installed in the gear
- Configure CloudSQL DB if it is added to a gear