Re-adding support for appending test error output.
Re-adding support for appending test error output.

ambrosebackflip/go2xunit,ambrosebackflip/go2xunit,ambrosebackflip/go2xunit,tebeka/go2xunit,tebeka/go2xunit,tebeka/go2xunit,tischda/go2xunit,tischda/go2xunit,tischda/go2xunit