Use TestCase rather than TransactionTestCase for API tests
Use TestCase rather than TransactionTestCase for API tests

This uses transactions for test isolation, rather than loading and then
blowing away the test fixtures for each individual test.

Running all the API tests now takes 4 seconds, rather than the 6 minutes
it took previously.

ebmdatalab/openprescribing,ebmdatalab/openprescribing,annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc,annapowellsmith/openpresc,ebmdatalab/openprescribing,ebmdatalab/openprescribing