Make autest happier during shutdown

Author: zwoop

src/proxy/http/remap/PluginFactory.cc

@@ -103,7 +103,7 @@ PluginFactory::~PluginFactory()
   _instList.apply([](RemapPluginInst *pluginInst) -> void { delete pluginInst; });
   _instList.clear();
 
-  {
+  if (!TSSystemState::is_event_system_shut_down()) {
     uint32_t elevate_access = 0;
 
     REC_ReadConfigInteger(elevate_access, "proxy.config.plugin.load_elevated");