DERBY-6352; Access denied ("java.lang.RuntimePermission" "modifyThread") highly intermittent, but e.g. in store.RecoveryAfterBackup test
  When we see a AccessControlException during shutdown in the notifyAll call, do nothing, which lets the Thread finish on its own.


git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1590817 13f79535-47bb-0310-9956-ffa450edef68