[TEST] split base settings in ClusterDiscoveryConfiguration between node and transport client

The default settings that are currently applied to the transport client are about discovery and gateway, modules that are not even loaded on the transport client. We can now remove the local gateway as it's the default one anyway. Also, let's make sure that the discovery setting is only applied to the node, as it is not relevant for transport client.
I personally like the fact that those settings were extracted from the code. The name (default) also indicate that these are defaults can be overridden. Don't feel strongly about it though - up to you whether to keep as is.