Connection.getEntityRef should throw ConnectionClosedException

[jd0-sag]

During the recent change to formalize the exception path through existing end-points and in-flight messages, we didn't also look at the paths to create new end-points.

Ideally, this would be documented to throw this new exception, as well.

[mathieucarbou]

@ChrisGreenaway @myronkscott : I am linking this with #215 also because we also ran into this issue. We are always using timed out invokations for voltron and when voltron closes the connection, we have no way to know and if we do a connection.getEntityRef(), it will block indefinitely.

So if we had #215 in place, we could know that the connection is closed and that we cannot use it.

[myronkscott]

I believe this to be occurring already. Confirm then close.