fix the load of config file of metric module. (apache#7040)

Author: SpriCoder

metrics/interface/src/main/java/org/apache/iotdb/metrics/config/MetricConfigDescriptor.java

@@ -104,9 +104,23 @@ public ReloadLevel loadHotProps() {
   private String getPropsUrl() {
     // first, try to get conf folder of standalone iotdb or datanode
     String url = System.getProperty(MetricConstant.IOTDB_CONF, null);
+    if (url == null) {
+      // try to get conf folder from IOTDB_HOME
+      url = System.getProperty(MetricConstant.IOTDB_HOME, null);
+      if (url != null) {
+        url += File.separator + "conf";
+      }
+    }
     // second, try to get conf folder of datanode
     if (url == null) {
       url = System.getProperty(MetricConstant.CONFIGNODE_CONF, null);
+      if (url == null) {
+        // try to get conf folder from CONFIGNODE_HOME
+        url = System.getProperty(MetricConstant.CONFIGNODE_HOME, null);
+        if (url != null) {
+          url += File.separator + "conf";
+        }
+      }
     }
     // finally, return null when not find
     if (url == null) {

metrics/interface/src/main/java/org/apache/iotdb/metrics/config/MetricConstant.java

@@ -25,7 +25,11 @@ private MetricConstant() {}
 
   static final String IOTDB_CONF = "IOTDB_CONF";
 
+  static final String IOTDB_HOME = "IOTDB_HOME";
+
   static final String CONFIGNODE_CONF = "CONFIGNODE_CONF";
 
+  static final String CONFIGNODE_HOME = "CONFIGNODE_HOME";
+
   static final String CONFIG_NAME = "iotdb-metric.yml";
 }