Set phase condition to free gas and free oil for water only cases

The water only case are now classified as free gas / oil in order to
avoid the usage of the rs / rv variable as these will be trivial. 

It is a bit misleading to call the water only case free oil or free gas. A more consistent solution may be to add a waterOnly condition to the phasePresence class in Blackoilphases and check for this in the variableState  function.

Runs a few iterations on Norne without NaNs