Add CI build for OpenLDAP integration

Early work to add tests using OpenLDAP for #46.

- [ ] install OpenLDAP
- [ ] enable memberOf, refint overlays
- [ ] seed with fixture data
- [ ] write tests specifically for OpenLDAP configuration
- [ ] connect to OpenLDAP instead of booting up ApacheDS for existing tests (fixing fixture mismatchs)

cc @jch 

The way you have it also works, but the `install` and `script` sections can be dried up a bit:

```sh
# if file exists, run it
[ -f ./script/install-$TESTENV ] && ./script/install-$TESTENV
[ -f ./script/cibuild-$TESTENV ] && ./script/cibuild-$TESTENV
```

Same with the above.

cc Travis docs [The Build Matrix](http://docs.travis-ci.com/user/build-configuration/) for reference.