return key in I18nUtil.getMessage  instead of null when no setting
[DS-1926] Move the fix to getMessage(String, Locale).

I noticed that getMessage(String) and getMessage(String, Context)
delegate to getMessage(String, Locale), so that is the proper place to
fix this.

Adjusted the log message as agreed, then added the name of the locale.
[DS-1926] Add a few unit tests.
Merge pull request #634 from mwoodiupui/DS-1926

[DS-1926] return key instead of null in I18nUtil.getMessage