The method `initiateChannel` on `TcpTransport` is explicit in that
channels can be connect asynchronously. All production implementations
do connect asynchronously. Only the blocking `MockTcpTransport`
connects in a synchronous manner. This avoids testing some of the
blocking code in `TcpTransport` that waits on connections to complete.
Additionally, it requires a more extensive method signature than
required for other transports.
This commit modifies the `MockTcpTransport` to make these connections
asynchronously on a different thread. Additionally, it simplifies that
`initiateChannel` method signature.
ee7eac8dc1