Add a test which fails if SES is not happy at NO_KNOWN_EXPLOIT_SPEC_VIOLATION level.

Since ES5/3 is deprecated, we no longer want to consider it OK for
SES to be unsafe on a browser we're testing on since there is no
fallback.

Therefore, add one test, cajajs-success, which loads Caja with
maxAcceptableSeverity set to NO_KNOWN_EXPLOIT_SPEC_VIOLATION instead of
NEW_SYMPTOM.

All other tests are left as-is, so that it is still possible to
troubleshoot specific problems even with SES failure.

@r5668

[felix8a, 2014-02-19 01:09:38]

lgtm