StorageTests#allTests flickers because an HSQL database lock file is not deleted when the server is shut down.

Caused by: java.sql.SQLException: The database is already in use by another process: org.hsqldb.persist.NIOLockFile@a76a2690[file =/home/hudsonagent/hudson_root/workspace/xwiki-enterprise-tests/xwiki-enterprise-test/xwiki-enterprise-test-storage/target/xwiki-enterprise-jetty-hsqldb-3.2-SNAPSHOT/database/xwiki_db.lck, exists=true, locked=false, valid=false, fl =null]: java.lang.Exception: checkHeartbeat(): lock file [/home/hudsonagent/hudson_root/workspace/xwiki-enterprise-tests/xwiki-enterprise-test/xwiki-enterprise-test-storage/target/xwiki-enterprise-jetty-hsqldb-3.2-SNAPSHOT/database/xwiki_db.lck] is presumably locked by another process.