Send empty/null response to Callback for exec commands that have no textual feedback.

[emilojkovic]

The ExecPipesExample uses an ExecWatch object and InputStreamPumper to execute a command in a pod.

When a command with textual feedback (ie. ls, pwd, echo "Hello World", etc.) is executed, the Callback object provided to the InputStreamPumper is correctly called with the response text. However, when a command with no feedback is executed (ie. cd, touch hello.txt, etc.) is executed, the callback function is not called at all.

Because of this, there is no signal that the command has finished executing. I would like to request for a null/empty string/some other default representing null to be sent back through the websocket & InputStreamPumper/Callback for commands that do not have textual feedback. This will standardize the way all commands are executed into a pod (it will always return something -- either the response text or a null) and will allow users to recognize when any command has finished executing.

[rohanKanojia]

@emilojkovic : Yeah, it makes sense to provide response in use cases where we don't get any textual feedback. This issue doesn't seem that complicated. Would be really awesome if you could submit a quick PR for this :)