Acceptance tests should use a real http server for node & yarn archive files

[mikrostew]

Right now the requests are being mocked, but the returned file is not a valid archive. This should be updated to use an actual http file server.

[charlespierce]

As mentioned in #1099, we should revisit this in light of mockito deprecating the SERVER_URL constant, as we will need some way to inject the appropriate server URL into the app when running tests.

One solution (not deeply investigated) may be to generate a hooks.json file for the tests that includes the server_url automatically.