Abstract the HostTracker class from host plugin test
    
    Implements a base class to help test LDAP based plugins.
    
    The class has been decoupled from the original host plugin test
    and moved to separate module ipatests.test_xmlrpc.ldaptracker.
    
    https://fedorahosted.org/freeipa/ticket/5032
    
    Reviewed-By: David Kupka <dkupka@redhat.com>