we are using the None value for some of the values that should be filled
by the configmap-etc template but as that template checks for empty values
and None is not counted, we are filling the tempest.conf with the wrong
values for auth and others
Instead use the null value for those so they get properly filled by the
template system into the appropiate values
Change-Id: I30528b1944722e9ce2e227b1b4dacae7635167ec
96aa69d131