MB-45214: Log shutdown due to stdin closure/shutdown message

It's good to know why we shutdown so log shut downs due to stdin
closure or a shutdown message in the memcached.log file (currently
it's just printed on stderr).

Change-Id: I1a07db85361b04014bf43f0246e0924559ac70b7
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/172766
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: BenHuddleston

daemon/memcached.cc

@@ -905,7 +905,12 @@ int memcached_main(int argc, char** argv) {
 
     if (Settings::instance().isStdinListenerEnabled()) {
         LOG_INFO_RAW("Enable standard input listener");
-        start_stdin_listener(shutdown_server);
+        start_stdin_listener([]() {
+            LOG_INFO_RAW(
+                    "Gracefully shutting down due to shutdown message or "
+                    "stdin closure");
+            shutdown_server();
+        });
     }
 
 #ifdef HAVE_LIBNUMA