Fixed oembed test

refs e04f55cce3

- added `nock.cleanAll()` so that there is no inter-test dependencies
- the failing test was successfully passing previously due to mocha's retry behaviour eventually exhausting nock request handlers that were set up in other tests and intended not to be called

test/api-acceptance/admin/oembed_spec.js

@@ -28,6 +28,7 @@ describe('Oembed API', function () {
 
     afterEach(function () {
         sinon.restore();
+        nock.cleanAll();
     });
 
     it('can fetch an embed', function (done) {