Parallelise tests by default #119

Tests are currently only run sequentially, unless t.Parallel() is called in a subtest. This will not scale as we increase the number of tests. The go test framework will parallelise tests in different packages by default, but the environments are completely isolated from each other so test suites cannot co-ordinate who is making what blueprint, or when to clean up docker containers. It would be good to figure out a way of doing this such that we have the ability to have at least some parallelisation by default to make it not scale with the number of tests quite so badly.

We may be able to do the package solution, provided we have some co-ordination mechanism for cleanup, even if it's just a naive "okay, all packages get their own namespace to work with". From a sheer complexity PoV this may actually be the best solution as it's easier to reason about (in that you don't need to care about who set up what, at the cost of making O(n) blueprints where n is the number of packages). Then the problem is how to slice and dice the existing tests. I tried this briefly, and we cannot split based entirely on feature, due to how the build tags work. If a directory has test files which are all build tagged up (e.g MSCs) then go test complains that there is nothing testable there (when the tag is not specified). We could add a dummy test file, but that is icky given we then expect new MSCs to add new directories causing the writer of the test to know about this. We could split based on protocol (CS API, SS API, ST API) but that reduces the amount of helper function sharing that can be done, which is typically per-feature (think registration, knocking). Currently all non-test functions share a global namespace as they are all in the same package which is a bit gross in terms of having a mess of global functions lying around.

Thoughts welcome.