Make it easier to deal with message queues in testing

[spladug]

CI environments have trouble with the POSIX message queues. This makes stuff that touches experiments or events really painful to work with. How can we improve this without detriment to production?

[spladug]

Lazily opening the message queue on first use could dodge the pain when events aren't actually used, but if they are we're still in the same world of hurt. It's also a bummer to do that because baseplate generally tries to feel out that its whole environment is ready during startup so that the process doesn't suddenly realize it's missing key environmental components after it started serving client requests.