Move thread join to finish callback for shutdown

- Shutdown is cleaner if we join the cache thread when the other threads
shut down.  Otherwise, the cache thread may keep running up until the
program exits, causing odd behavior.

modules/realm_stages/src/tileing.cpp

@@ -46,11 +46,6 @@ Tileing::Tileing(const StageSettings::Ptr &stage_set, double rate)
 
 Tileing::~Tileing()
 {
-  if (m_tile_cache)
-  {
-    m_tile_cache->requestFinish();
-    m_tile_cache->join();
-  }
 }
 
 void Tileing::addFrame(const Frame::Ptr &frame)
@@ -346,9 +341,14 @@ void Tileing::reset()
 
 void Tileing::finishCallback()
 {
+  if (m_tile_cache)
+  {
+    m_tile_cache->requestFinish();
+    m_tile_cache->join();
+  }
+
   // Trigger savings
   saveAll();
-
 }
 
 Frame::Ptr Tileing::getNewFrame()