Support for LDAP tests

* Allow Beeswax connections to optionally use LDAP
* Run custom cluster tests from the aux repo, if it exists

Change-Id: I054af64e030ad0cd722ae8dd75afda9c58ea2913
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2547
Reviewed-by: Ishaan Joshi <ishaan@cloudera.com>
Tested-by: jenkins