Adding --update-snapshots to the maven test command

This will force maven to update any cached snapshot library that it needs. While the compile-and-unit-test job would have done this previously, the .m2 cache is not necessarily shared between runners of these two jobs (if two different runners pick up the jobs).

This maybe could be leading to some issues, though I'm not certain that it is a problem. However, this seems like a fairly low weight change without much harm, so it is worth the try.