Cleanup of the CryptoTests class naming. HMAC success/failure tests for Handshake packets.

In response to issue: https://github.com/WhisperSystems/Signal-iOS/issues/30

The CryptoUtilTest class was named as such when the current CryptoTools class was named CryptoUtil. I've cleaned this up and added another test so that all of the CryptoTools methods are getting coverage (for what it's worth).

Also added some testing to verify HMAC is being handled not-terribly on handshake packets, since there is a reasonable amount of logic in there.