We make the binary that should be copied into the container configurable via a build time `ARG`. This will allow us to reuse the same `Dockerfile` once we write more tests.
Additionally, this allows us to remove some of the directory switching and creation code. In order to not send the entire repository over to the docker daemon as a build context, we introduce a `.dockerignore` file that only allows select binary to be sent over.
The downside of this is that we need to extend this ignore file every time we add a new test. This shouldn't happen very often though and is easily discovered because the building of the docker container will fail.
Node and browser tests take a little bit longer to spin up in the interop tests. The multidim-interop can tell the tests to increase the timeout when testing against these targets, but the test itself needs to use the passed in value.
This updates the test code to handle the new test_timeout option. See https://github.com/libp2p/test-plans/issues/107
