TCK: Issue2648IT: IllegalStateException should be thrown if current response has already been committed (During Ajax Request)

Background Issue: https://github.com/eclipse-ee4j/mojarra/issues/2652

In a nutshell: if handling an ajax request, we should throw an IllegalStateException during a second redirect (if the one has been committed).

This is apparent in the MyFaces code below. We just complete the response in the ajax case ("isPartialRequest") without checking if it's been completed already.

https://github.com/apache/myfaces/blob/93a47f3c78716f0ff3c01227ee1cd5972aeb965b/impl/src/main/java/org/apache/myfaces/context/servlet/ServletExternalContextImpl.java#L590-L600