Replace ApacheDS/Ladle test server with OpenLDAP in CI

[mtodd]

Found some prior art getting OpenLDAP running for TravisCI here: https://github.com/cloudfoundry/uaa/blob/master/.travis.yml#L33

I don't know if we can replace ApacheDS/Ladle completely (local tests, for instance), but it would be great to run all tests against OpenLDAP regularly.

[mtodd]

#48 was merged but instead of replacing ApacheDS/ladle, it added OpenLDAP to test alongside ApacheDS so now all our tests are running against both. Was also able to speed up the ApacheDS tests and reduce complexity of the fixtures.

Going to keep ApacheDS for the time being since it means running tests standalone without having to boot OpenLDAP vagrant boxes/standalone. May revisit later.