LogDecommissioningNodesStatus method in DecommissioningNodesWatcher uses StringBuilder to append status of all
decommissioning nodes for logging purpose.
In the case of large number of decommissioning nodes, this leads to OOM exception. The fix scopes StringBuilder so that in case of memory pressure, GC can kick in and free up the memory.
This is supposed to fix a bug introduced in https://issues.apache.org/jira/browse/YARN-4676