Tweak Dockerfile
Tweak Dockerfile

- don't use an 'ubuntu' user (won't work in concourse)
- use the standard postgresql install (9.3 is gone)

Signed-off-by: Colin Obyrne <c47cc0033a0530c1ec004ae8db451730368aa030@pivotal.io>

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh