Please make it possible to run tests without Docker

We'd like to package aiomcache for Gentoo. As part of the packaging process, we need to be able to run the test suite. While we can reasonably easily spawn a local memcached instance for testing, we can't use Docker for testing (both because it can't work without direct Internet access and because it poses security issues).

Unfortunately, the test suite seems to be really tightly tied to using a Docker container. Could you please make it possible to use an externally running memcached server instead?