Set the TTS voice name for the default language.

This changes makes the initial, default language set and
the #setLanguage call with the default language as input
exactly the same.

Previously, the requests made after the initial default language
set were missing the name of the default voice.

+ Some tests clean-up. Some of them fail due to issues with
Locale#toLanguageTag upper-casing the variant field.

Change-Id: I5470617007fe45462b7198bf62a03eb5fe47a590