HBASE-24675: On Master restart all servers are assigned to default rsgroup

Closes #2053

Signed-off-by: Viraj Jasani <vjasani@apache.org>

Author: arshadmohammad

hbase-rsgroup/src/main/java/org/apache/hadoop/hbase/rsgroup/RSGroupInfoManagerImpl.java

@@ -525,7 +525,8 @@ private synchronized void refresh(boolean forceOnline) throws IOException {
 
     // This is added to the last of the list so it overwrites the 'default' rsgroup loaded
     // from region group table or zk
-    groupList.add(new RSGroupInfo(RSGroupInfo.DEFAULT_GROUP, getDefaultServers(), orphanTables));
+    groupList.add(
+        new RSGroupInfo(RSGroupInfo.DEFAULT_GROUP, getDefaultServers(groupList), orphanTables));
 
     // populate the data
     HashMap<String, RSGroupInfo> newGroupMap = Maps.newHashMap();
@@ -684,9 +685,15 @@ private List<ServerName> getOnlineRS() throws IOException {
 
   // Called by ServerEventsListenerThread. Presume it has lock on this manager when it runs.
   private SortedSet<Address> getDefaultServers() throws IOException {
+    return getDefaultServers(listRSGroups());
+  }
+
+  // Called by ServerEventsListenerThread. Presume it has lock on this manager when it runs.
+  private SortedSet<Address> getDefaultServers(List<RSGroupInfo> rsGroupInfoList)
+      throws IOException {
     // Build a list of servers in other groups than default group, from rsGroupMap
     Set<Address> serversInOtherGroup = new HashSet<>();
-    for (RSGroupInfo group : listRSGroups() /* get from rsGroupMap */) {
+    for (RSGroupInfo group : rsGroupInfoList) {
       if (!RSGroupInfo.DEFAULT_GROUP.equals(group.getName())) { // not default group
         serversInOtherGroup.addAll(group.getServers());
       }