Explore running crossbar outside of docker for tests

[BrianJKoopman]

When integration tests were initially developed, running crossbar in docker seemed like the easiest option. Now that we have developed fixtures for starting things like agents automatically for each test, likely we could write a fixture for starting a crossbar server outside of a docker container.

This could allow us to drop the dependency on running docker for running the tests, which is appealing. It could also reduce the amount of time spent waiting for containers to start/stop during integration testing.