8352428: GenShen: Old-gen cycles are still looping

Reviewed-by: wkemper, shade

src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp

@@ -188,6 +188,7 @@ void ShenandoahHeuristics::record_cycle_end() {
 
 bool ShenandoahHeuristics::should_start_gc() {
   if (_start_gc_is_pending) {
+    log_trigger("GC start is already pending");
     return true;
   }
   // Perform GC to cleanup metaspace

src/hotspot/share/gc/shenandoah/shenandoahRegulatorThread.cpp

@@ -80,6 +80,7 @@ void ShenandoahRegulatorThread::regulate_young_and_old_cycles() {
           }
         } else if (_old_heuristics->should_resume_old_cycle() || _old_heuristics->should_start_gc()) {
           if (request_concurrent_gc(_heap->old_generation())) {
+            _old_heuristics->cancel_trigger_request();
             log_debug(gc)("Heuristics request to resume old collection accepted");
           }
         }