Addresses #103 and other shutdown behavioral issues

- Use a base common TestCase for all tests but integration tests

Even though the Connection.Close frame was being added to the buffer, it was never written. Change to an RPC call and wait for Connection.CloseOk to be returned.

Faster message body retrieval

allow for username and password to be default again - fixes #96

This should significantly speed up receiving large messages (10x in my
application).

- If heartbeat is not configured, used the server
- If it is configured and is 0 or the server is 0, turn it off
- Otherwise use the client requested value