[BuildStream] Breaking change: removing auto-init functionality

Hello list!

I'm proposing a breaking change to remove BuildStream's "auto-init"

functionality, based on Tristan's assertion that no one minds if it goes away.

I'm sending this message just in case.

tvb> I don't suspect anyone is going to mind removing the prompt asking whether

tvb> you want to do the bst init thing.

https://gitlab.com/BuildStream/buildstream/merge_requests/957#note_122726370

You may be wondering what "auto-init" is. Well currently if you invoke

BuildStream and it can't determine the current project, it will offer to create

a new project in the current directory:

    $ bst show app.bst

    A project was not detected in the directory: /tmp

    Would you like to create a new project here? [y/N]:

I recently added an option to buildstream.conf to disable this.

I'm now proposing to remove this entirely, and replace it with a hint that you

could run 'bst init' if you wanted to create a project.

Why am I proposing this? Minor reasons really.

- It would remove a small amount of complexity from the project.

- I'm generally for tips and against yes/no prompts.

- If we were to ever introduce a global '--force' parameter to BuildStream,

  then auto-init would be a weird thing to do. For example

  'bst --force checkout app.bst' might create a new project if we couldn't

  determine which one was meant.

Please say if you object.

Cheers!

Angelos

P.S.

It was originally introduced here:

https://gitlab.com/BuildStream/buildstream/commit/1f57e598a3f286716f197fb4a10f2515ce562ed8

It wasn't explicitly asked for in the related issue, I'll post a link to this

ML thread there anyway:

https://gitlab.com/BuildStream/buildstream/issues/342