Zip up the MP Metrics TCK surefire reports for easy download

Use the maven-assembly-plugin to zip up the target/surefire-reports/TEST-**.xml files. CI jobs can then be configured to archive the zip, making it easy to pull down all the files when preparing compliance certification documents, e.g.

https://github.com/wildfly/certifications/tree/MP4.1

https://github.com/wildfly/certifications/tree/MP5.0

The other MP TCKs use TestNg which creates a single summary xml file that we can use, but MP Metrics uses junit, which does not.