External Directory configuration should support searching from the Base DN

Users are no longer able to configure their searches to use just the basedn when configuring external directories from the PE 3.7.0 console. In PE 3.7.0, we require all users to configure both a group and user rdn. It's not uncommon for an organization to deploy users to different OU's in order to signify different locations, job classifications, etc. One was able to configure this in rubycas in previous releases of Puppet Enterprise.