Fix TTS tests.

Fix breakages steaming from recent changes:
- onGetLanguage is no longer called anywhere (it's used in API <= 17),
tests for it no longer apply.
- onLoadLanguage is called as item on synthesis thread queue. To return
value to client asap, onIsLanguageAvailable is called as well - added
missing expectations for mocks.

Change-Id: I205bc406f085e2c2f7e98f8495ddb96ad3701b97