Comment 2 for bug 1085823

IIRC this was done to fix a problem with the testing lab network topology (but I don't think that topology is *that* specific so let's think this through before we revert the fix for this): the master nodegroup has an interface (interfaces are auto-populated) that actually connects to the separate cluster's network. Hence if we use all the interfaces (as opposed to only the managed interface) to do the match in find_nodegroup(), we would always get the master nodegroup, even for a node connecting from the separate cluster's network.