install: remove adhoc api.Backend.ldap2 (dis)connect
    
    Remove adhoc connects and disconnects of api.Backend.ldap2. Connection
    should be established only at the start of the script, destroyed at the
    end of the script and re-established when directory server is restarted.
    
    https://fedorahosted.org/freeipa/ticket/6461
    
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Jan Cholasta <jcholast@redhat.com>