Add CI build for OpenLDAP integration

Reopening #47 against `dev-v2` since this is targeting v2.0 release.

Early work to add tests using OpenLDAP for #46.

- [x] install OpenLDAP
- [x] enable memberOf, refint overlays
- [x] seed OpenLDAP with fixture data
- [x] rewrite existing tests to use common seed
- [x] boot ApacheDS with common seed before all tests, teardown after all tests (no re-starting)
- [ ] add vagrant VM definition for running OpenLDAP on local environment

cc @jch 

Why no merge with `GitHub::Ldap.server_options` like above?