Fix crash on shutdown when update in progress.

The ActionProcessor destructor normally calls the ProcessingStop method
on the delegate. For the UpdateAttempter this call re-schedules a new
update attempt on a half-destroyed update_attempter instance, crashing
update_engine on SIGTERM when the ActionProcessor was running.

This patch inhibits the ActionProcessor from notifying the delegate of
the processor stopping when destroying the update_attempter instance.
It also fixes the declaration order of the dbus_adaptor_ and disables
its usage during daemon shutdown.

Bug: 24989397
TEST=start update-engine; (update_engine_client --update &); sleep 6; stop update-engine; tail /var/log/update_engine.log
TEST=FEATURES=test emerge-link update_engine

Change-Id: I0a40067f63e89759ff80c79cecb6f89b10dba0c2
diff --git a/daemon.h b/daemon.h
index 5aef8c5..66841f6 100644
--- a/daemon.h
+++ b/daemon.h
@@ -31,6 +31,7 @@
 class UpdateEngineDaemon : public brillo::DBusDaemon {
  public:
   UpdateEngineDaemon() = default;
+  ~UpdateEngineDaemon();
 
  protected:
   int OnInit() override;
@@ -46,9 +47,11 @@
   // the main() function.
   Subprocess subprocess_;
 
-  std::unique_ptr<RealSystemState> real_system_state_;
   std::unique_ptr<UpdateEngineAdaptor> dbus_adaptor_;
 
+  // The RealSystemState uses the previous classes so it should be defined last.
+  std::unique_ptr<RealSystemState> real_system_state_;
+
   DISALLOW_COPY_AND_ASSIGN(UpdateEngineDaemon);
 };