Local ActiveDirectory integration testing

We're unable to run ActiveDirectory in CI at this time, so I documented how to run tests against a local AD instance. I also added additional tests for the AD membership validator. Assuming a similar seed file is loaded into AD, we'll be able to run these tests locally.

cc @mtodd @jameswhite 
`ad-env.sh` should probably be `activedirectory/env.sh` right?