update hearbeat thread num = 1 (#1029)

* move updateTaskState into try/catch block in case of exception

* fix NPE

* using conf.getInt instead of getString

* for AbstractZKClient, remove the log, for it will print the same log message in createZNodePath.
for AlertDao, correct the spelling.

* duplicate

* refactor getTaskWorkerGroupId

* add friendly log

* update hearbeat thread num = 1

dolphinscheduler-common/src/main/java/org/apache/dolphinscheduler/common/Constants.java

@@ -368,7 +368,7 @@ public final class Constants {
     /**
      * heartbeat threads number
      */
-    public static final int defaulWorkerHeartbeatThreadNum = 5;
+    public static final int defaulWorkerHeartbeatThreadNum = 1;
 
     /**
      * heartbeat interval
@@ -431,7 +431,7 @@ public final class Constants {
     /**
      * default master heartbeat thread number
      */
-    public static final int defaulMasterHeartbeatThreadNum = 5;
+    public static final int defaulMasterHeartbeatThreadNum = 1;
 
 
     /**