Core and Simple Cache API integration tests

[joeshaw]

Currently Viceroy doesn't support the Core Cache API (added in #47) other than stubs. Once there is something more complete we should add an integration test for it there.

Basis can be the example program in _examples/corecache.

[joeshaw]

Ditto for Simple Cache API.

[joeshaw]

Viceroy support was added in 0.14.0. https://github.com/fastly/Viceroy/blob/main/CHANGELOG.md#0140