Failing test for multiple registry cache bug

There is a bug with how the cache in npm works.

If you use multiple registries it will sometimes install
a module from the cache but that module would be wrong
because it installed a module from the cache with a different
registry.

What we expect is that when we do

`npm install --registry=foo module@version`

That the package.json in `node_modules/module/package.json`
would contain the package.json from the foo registry.

i.e. we expect `_resolved` to contain the `foo` registry.

If it does not then we get a cascading bug where if you
run `npm shrinkwrap` it will put the wrong `"resolved"`
field in the shrinkwrap, i.e. a `"resolved"` field pointing
to a different registry then what you expected

cc @othiym23