cli: feedback is required for every command

[Yorkie Makoto]

The commands clean and install don't give any feedback, we need to make sure every command will give a response.

[feely]

@yorkie Should be fixed by #750.

[Yorkie Makoto]

Not yet, run pipcook clean doesn't give any feedback.

[feely]

Not yet, run pipcook clean doesn't give any feedback.

Not released. It will be published with 2.0.0-rc.3 tonight.