graphdb: initialize the database semi-idempotently on every connection.

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: erikh)

Docker-DCO-1.1-Signed-off-by: Erik Hollensbe <github@hollensbe.org> (github: jfrazelle)
Bump version to v1.4.0

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)