Sorry for the trouble. Interestingly enough if you look at Index of /schema/arquillian you will notice last change to the file was made in November 2016 which makes me even more confused. We will investigate.
After a quick investigation, it turned out you are most likely a victim of a wrong example created in GlassFish project (already fixed). That was, in fact, the only place we could still find the wrong schema in arquillian.xml.
Since a long time we had _ in place, but probably, the old file was stored on the server as well, until recently when it was probably deleted causing you headaches. We also validated other projects and made sure our Forge Addon also generates the right one. Thanks for reporting!
This seems consistent as the mentioned message has appeared consecutive to the replacement of the org.glassfish.jersey.* artifacts by org.apache.cxf.* ones. I don't pretend to really understand what exactly might have happened but since you're diagnosting a wrong Glassfish dependency, I reckon it must have to do with that, as this is exactly what I got rid of.
Many thanks for the explanation.