MGM: LOG: GroupBalancer downgrade no groups left to balance to debug

This happens regularly, and also can be easily checked via the status commands,
do not log at WARN level

Signed-off-by: Abhishek Lekshmanan <abhishek.lekshmanan@cern.ch>

Author: theanalyst

mgm/GroupBalancer.cc

@@ -438,7 +438,7 @@ GroupBalancer::GroupBalance(ThreadAssistant& assistant) noexcept
 
     if (!FsView::gFsView.mSpaceGroupView.count(mSpaceName.c_str())) {
       FsView::gFsView.ViewMutex.UnLockRead();
-      eos_static_warning("msg=\"no groups to balance\" space=\"%s\"",
+      eos_static_debug("msg=\"no groups to balance\" space=\"%s\"",
                          mSpaceName.c_str());
       break;
     }