Nightly tests: TestStressThreadBackup

[David Smiley]

org.apache.solr.handler.TestStressThreadBackup appears to fail in every
"nightly" main build:
http://fucit.org/solr-jenkins-reports/failure-report.html

~ David Smiley
Apache Lucene/Solr Search Developer
http://www.linkedin.com/in/davidwsmiley