Add support for Erlang/OTP Junit format

The Common Test framework in Erlang/OTP can create Jenkins/Hudson
compatible Junit reports since R15B. In xunit 1.54 these files are
correctly consumed and rendered by the xUnit plugin.

However in more recent versions the files are not parsed correctly due
to some extra attributes. This adds support for these attributes. The
standard Jenkins Junit plugin consumes these files correctly.