DERBY-6352; Access denied ("java.lang.RuntimePermission" "modifyThread") in store.RecoveryAfterBackup test
  adding try/catch code to provide more information when this happens


git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1531721 13f79535-47bb-0310-9956-ffa450edef68