Stop using `--no-lockfile` / `--no-shrinkwrap` by default? 🤔

I think it is about time that we considered removing the `--no-lockfile`/`--no-shrinkwrap` defaults for `yarn` and `npm` scenarios.

As of #409, it is _possible_ to avoid if you'd like (that hook allows you to customize the options explicitly, with no default values) but the default of "ignoring lockfile" seems a bit wrong to me nowadays. I'd like to see us be able to have most scenarios use the lockfile and just bump the specific dependencies in the scenario. In my opinion that much more closely resembles what folks will **actually** do in practice.

For example, I would like to have `ember-cli` use `ember-try` scenarios for its floating dependencies test and have that scenario look like:

```js
{
name: 'floating-dependencies',
npmOptions: ['--no-lockfile'],
}
```

Thoughts?