behavior with maps

[kevinburkesegment]

I guess I expected based on the Map abstraction that you could deserialize config into either a map or a struct. One of the first tests I wrote did this:

       source := NewKubernetesConfigMapSource("./testdata/configmap")
       base := make(map[string]string)
       mp := makeNodeMap(reflect.ValueOf(base), reflect.TypeOf(base))
       if err := source.Load(mp); err != nil {
               t.Fatal(err)
       }

Which "worked" but produces a panic if you try Loader.Load.

We should maybe try to make more clear that you should only be passing structs, maybe by also panicking further down.