Change `add_data_node` so that host parameter is required. If the host
parameter is not provided, or is `NULL`, an error will be printed.
Also change logic for how the default value for `port` is picked. Now
it will by default use the port given in the configuration file.
The commit update all the result files, add the `host` parameter to all
calls of `add_data_node` and add a few tests to check that an error is
given when `host` is not provided.
6e9f644714