Add an option to use AWS instance address in a PostgreSQL connection string.

When PostgreSQL is running inside the docker container, it should provide
the address of the host it's running on and not the address from inside
of the container to the outside world.

postgres0.yml

@@ -1,4 +1,5 @@
 loop_wait: 10
+aws_use_host_address: "on"
 etcd:
   scope: batman
   ttl: 30