8165292: The gc+task logging is repeated a lot, decreasing the usefulness of -Xlog:gc*=info

Separate number of workers used debugging information from adaptive worker sizing log messages.

Reviewed-by: ehelin, sjohanss, jmasa

hotspot/src/share/vm/gc/cms/concurrentMarkSweepGeneration.cpp

@@ -3511,6 +3511,7 @@ bool CMSCollector::do_marking_mt() {
                                                                   conc_workers()->active_workers(),
                                                                   Threads::number_of_non_daemon_threads());
   num_workers = conc_workers()->update_active_workers(num_workers);
+  log_info(gc,task)("Using %u workers of %u for marking", num_workers, conc_workers()->total_workers());
 
   CompactibleFreeListSpace* cms_space  = _cmsGen->cmsSpace();