java: improve use of WrappedTargetException to set cause properly

since we introduced the new constructors that pass the cause all the
way up to java.lang.Throwable.
Also simplify some exeception printing sites, because Throwable
will correctly print out child exceptions for us.

Change-Id: Ibbecce3c6f971fbc80d6de2052ab4f33a4503c0a