[Reviewer: Alex] Don't use localhost and don't set Ralf for all-in-one nodes

Alex, can you review this change to use the local ip instead of localhost for the all-in-one nodes. I've also changed it so the ralf_hostname is no longer set for all-in-one nodes
You don't actually need this change at all (since a shell variable with a blank value is treated almost identically to an unassigned one).

However if you do decide to keep it, don't bother with `.nil?` bit. In ruby `nil` evaluates as `false` in boolean contexts. Though it would be nice to have some syntactic sugar (so you could just write `<%= option "ralf_hostname", @ralf %>` or similar).