Consolidate external member code into two functions in baseldap.py
    
    External members (users and hosts) are assumed when doing member
    management on certain attributes. If the member isn't in IPA it
    is assumed to be external. When doing member management we need
    to sift through the list of failures and pull out all those
    that were simply not found in IPA.
    
    https://fedorahosted.org/freeipa/ticket/1734