Fix test failures on docker 1.1.2

Some background in #328, but I've seen the integration test suite failing on two tests (`test_project_up_recreates_containers`, `test_recreate_containers`) for a while now, ever since I upgraded to docker 1.1.x.

Changing the path from `/var/db/` to `/etc/` fixes this, which I think is an improvement for now (so that the tests are still useful for catching other issues).

The second part of this change is to add a `container.get()`.  This uses dotted notation and performs an `inspect_if_not_inspected()` on each call, removing the need to call it everywhere, and providing a nicer interface for fetching other container data if there isn't an existing property for it.