SOLR-6650 - Add optional slow request logging at WARN level
Merge branch 'trunk' of https://github.com/mewmewball/lucene-solr into trunk

# By Jan Høydahl
# Via Jan Høydahl
* 'trunk' of https://github.com/mewmewball/lucene-solr:
  SOLR-6647: Bad error message when missing resource from ZK when parsing Schema