fix thread name for pool_poolherder, add it for pool_herder

bin/varnishd/cache/cache_pool.c

@@ -190,7 +190,7 @@ pool_poolherder(void *priv)
 	struct pool *pp;
 	uint64_t u;
 
-	THR_SetName("pool_herder");
+	THR_SetName("pool_poolherder");
 	(void)priv;
 
 	nwq = 0;

bin/varnishd/cache/cache_wrk.c

@@ -438,6 +438,8 @@ pool_herder(void *priv)
 
 	CAST_OBJ_NOTNULL(pp, priv, POOL_MAGIC);
 
+	THR_SetName("pool_herder");
+
 	while (1) {
 		/* Make more threads if needed and allowed */
 		if (pp->nthr < cache_param->wthread_min ||