Functions don't work with TrafficManager when added as external endpoints

After reading #214 I was convinced that I needed to add my Function as an external endpoint for the TrafficManager integration to work.

However, I never got it to work that way and instead got the 404 page every time I tried to access it via the TrafficManager.

When the Function is added as an Azure AppService endpoint instead then it magically works.

Steps to reproduce:

1. create a function app with consumption based AppService plan
2. create an HTTP Triggered function (with access level "anonymous") which returns HTTP 200 OK with body "Hello"
3. create a function proxy to redirect "/" to the function URL backend
4. ensure that http://.azurewebsites.net returns the "Hello" with HTTP 200 OK as expected

Now that your function is working and returning something on the root path, set up a TrafficManager with the function as an endpoint:

1. create a new TrafficManager with DNS name .trafficmanager.net
2. add the function as an external endpoint

FAIL: When you try to access it via http://.trafficmanager.net you will get a 404 page

To make it work, add the function as an Azure AppService endpoint instead.

PASS: When you try to access it via http://.trafficmanager.net it should work now

Not sure if that is the expected behaviour, but it's definitively confusing. It it is by design not working as an external endpoint, it would be nice to get a warning in the Portal GUI at least when trying to add a Function as an external endpoint