Prompt to automatically execute `tns test init` on `tns test`

[DimitarTachev]

Describe the solution you'd like
After #4381, the test command will tell you to run tns test init if your app is not ready for unit testing. It will be better if we interactively ask the user and init the app without exiting the test command.

Additional context
We should also think about providing this in the VSCode extension.