Investigate possible server shutdown hang on shutdown

[rdig]

As I've noted in the global teardown file of the colonyDapp integration tests, I've ran into an issue where the whole process doesn't exit cleanly: https://github.com/JoinColony/colonyDapp/blob/7410f9bcb9b30ffbd0cbd027c9342494cb9d5788/integration-testing/utils/integration-testing-teardown.js#L37-L52

I have to hard exit the jest test runner using process.exit().

I suspect this is has something to do with trufflepig since this only started to happen after I've added it to the integration tests setup.

Maybe it's something to do with how I use it / configure it, or maybe it's something else entirely.

In any case it requires some digging.