fix base64 test
Test fixes.

- Readded all the browsers to Zuul config.
- Fixed b64 encoding test, typo + we're better off asserting the actual b64
  encoding.
- Got rid of the base64-js dependency only needed by the test described above.
- Running iPhone tests for 6.0 and above due to some really weird timeout
  issues on older iPhone emulators, where tests do succeed when run
  individually (and fail on no other browser even together).