dhis2: Create a clean, controlled set of integration tests

[josephjclark]

dhsi2 has a very useful set of integration tests

but they keep failing for reasons out of our control, because of changes in the backend.

This issue is to think about how we can stabilise the tests so that we can run them reliably.

Options/thoughts:

• Can we host our own dhis2 sandbox where we're in full control of the state?
• Can we redesign the test data to be totally standalone? So we create all the resources we need, then edit them, then remove them?
• Can we have some kind of setup step which initialises the sandbox with the resources we need, then run integration tests against those pre-created resources?