SOLR-6673 added MDC based logging in a few places but we have a lot of ground to cover.
- Threads created via thread pool executors do not inherit MDC values and those are some of the most interesting places to log MDC context.
- We must expose node names (in tests) so that we can debug faster
- We can expose more information via thread names so that a thread dump has enough context to help debug problems in production
This is critical to help debug SolrCloud failures.