Upgrade log4j2 to the current version, presently 2.12.1

First, we still have some interesting logging bleed leaks that we can't account for, it's always possible anyway and I'm an optmist

Second, there's a long discussion about leaked threads (albeit under Tomcat) and some vague references to rethinking how threads are handled in Log4J2. We already have a hack to not fail on leaked logger threads in our tests, perhaps this will address that need.

Third, "Version 2.12.0 introduces support for accessing Docker container information " which may be increasingly interesting.

I won't get to this soon, so anyone who wants to pick it up please do. Might be wise to wait until after the 8.4 branch is cut, I'm always a little leery of upgrading things just before a release.