Add test for invalid data url, reorganize the other tests
Add test for invalid data url, reorganize the other tests

Added the test for invalid data url, reorganized the other tests,
removing those that were unnecessary.

mozilla-services/pageshot,mozilla-services/pageshot,mozilla-services/screenshots,mozilla-services/screenshots,mozilla-services/pageshot,mozilla-services/pageshot,mozilla-services/screenshots,mozilla-services/screenshots