Special case late pool stats push also for DBG_VCLREL

If the DBG_VCLREL is in effect and there are unpushed pool stats, make
sure that some thread is waking up to perform the late push. This should
help with stability for VTC test cases using the DBG_VCLREL flag.

bin/varnishd/cache/cache_wrk.c

@@ -389,7 +389,17 @@ Pool_Work_Thread(struct pool *pp, struct worker *wrk)
 			pp->nidle++;
 			do {
 				// see signaling_note at the top for explanation
-				if (wrk->vcl == NULL)
+				if (DO_DEBUG(DBG_VCLREL) &&
+				    pp->b_stat == NULL && pp->a_stat->summs)
+					/* We've released the VCL, but
+					 * there are pool stats not pushed
+					 * to the global stats and some
+					 * thread is busy pushing
+					 * stats. Set a 1 second timeout
+					 * so that we'll wake up and get a
+					 * chance to push stats. */
+					tmo = wrk->lastused + 1.;
+				else if (wrk->vcl == NULL)
 					tmo = 0;
 				else if (DO_DEBUG(DBG_VTC_MODE))
 					tmo =  wrk->lastused+1.;