classes-recipe: npm: Complain immediately if npm-shrinkwrap.json is too old

classes-recipe: npm: Complain immediately if npm-shrinkwrap.json is too old

Rather than emitting:

 Exception: KeyError: 'packages'

and a stack trace, let's fail immediately if lockfileVersion implies
that the npm-shrinkwrap.json file isn't compatible.

The documentation[1] doesn't make it clear which lockfileVersions are
guaranteed to contain "packages". I have lockfileVersion 1 files
without. Running npm 7.5.2 generates npm-shrinkwrap.json files with
lockfileVersion 2 and "packages", so I've set the minimum to be 2.

[1] https://docs.npmjs.com/cli/v7/configuring-npm/package-lock-json

Signed-off-by: Mike Crowe <mac@mcrowe.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>