Add Logger::log_event_uuid accessor

Change-Id: I666b5fec78664919d55550fd2ddc9e7a359633a8
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/events/logging/log_writer.h b/aos/events/logging/log_writer.h
index 6fb1bfa..265513f 100644
--- a/aos/events/logging/log_writer.h
+++ b/aos/events/logging/log_writer.h
@@ -182,6 +182,10 @@
     });
   }
 
+  // Returns the current log event UUID.  This is randomly assigned when the log
+  // starts or restarts.
+  const UUID &log_event_uuid() const { return log_event_uuid_; }
+
  private:
   // Structure to track both a fetcher, and if the data fetched has been
   // written.  We may want to delay writing data to disk so that we don't let