Tor reports that NeonLockStore::stopTicker() m_pTickerThread->join()
can deadlock with TickerThread running NeonLockStore::refreshLocks().

This can be avoided by copying m_pTickerThread to the stack, and
releasing the m_aMutex before calling join().

Change-Id: I387f83a530c5b893f79fa677b1092e0902c8af65