Wait for connect to finish sending all data

[thayama]

Goroutines created in connect, transfer data from a handler to telnet client. However, as there's no synchronization between the goroutine and the telnet server, there's a case where the server sends a prompt before the goroutines finished all transmissions.

This fix assure that the telnet server waits until all data are sent to the client, before sending a prompt.

[thayama]

I've found an issue that the one last byte generated by telsh.Handler is sent after the shell prompt. Currently, there is a race condition between handler.Run() and go func launched in connect().

I've added channels to wait for go funcs launched in connect() to finish their jobs.

[mligor]

My vote for this pull request