[lldb/test] s/add_no_ack_remote_stream/do_handshake

These two functions are doing the same thing, only one of them is
sending the packets immediately and the other "queues" them to be sent
later. The first one is better as in case of errors, the backtrace will
point straight to the place that caused them.

Modify the first method to avoid duplication, and ten standardize on it.