Start with a fresh folder and copy a hapi.properties into it. It will be mounted into the container.
Carefully make sure your hapi.properties looks like this:
# add postgres
datasource.driver=org.postgresql.Driver
datasource.url=jdbc:postgresql://db:5432/hapi
hibernate.dialect=org.hibernate.dialect.PostgreSQL95Dialect
datasource.username=admin
datasource.password=admin