Update Postgresql for use with newest cloud controller

When you attempt to bind one of the community-provided services in this repository to an application in CloudFoundry release 151, you receive the error "CFoundry::ServerError: 10001: Service broker error: Malformatted request"

Investigating this further, it appears that the service broker API has significantly changed in the latest cf-releases and thus, service gateways need to be updated accordingly.  Using the cf-services repository (mysql gateway) as a template, this pull request makes the updates required to get Postgresql working as a Cloud Foundry contrib service once again.

The other services will have to be done in future pulls.