Tests: Configure JUL logging based on VERBOSE flag [LUCENE-6189]

I propose that LuceneTestCase check if VERBOSE is false, and if so then do this: `Logger.getLogger("org.apache.lucene").setLevel(Level.SEVERE)`.

This will allow test classes to grab a logger and log to it at appropriate levels without having to guard each log line with `if (VERBOSE) ...`

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Migrated from [LUCENE-6189](https://issues.apache.org/jira/browse/LUCENE-6189) by David Smiley (@dsmiley)

Start in LuceneTestCase and inspect how the VERBOSE flag is handled during test setup. Configure the org.apache.lucene logger for non-verbose runs as described, then verify that tests still pass and that verbose runs retain their logging.

Written by the indexing model from the issue text.