Ensure that broadcast/request/stream/wait_for cannot be called prior to running the endpoint.

[pipermerriam]

What was wrong?

It should result in an error to call any of the following APIs if the endpoint is not yet running.

• EndpointAPI.broadcast
• EndpointAPI.request
• EndpointAPI.stream
• EndpointAPI.wait_for

How can it be fixed?

Add tests to ensure these all throw friendly useful errors when called prior to the endpoint being running or after the endpoint has stopped. Ideally we figure a way to do this with as little runtime overhead as possible.