HBASE-21007 Memory leak in HBase REST server

Close the scanner leak in rest server when using the limit number of rows.

Example: when using uris like

        /sometable/*?limit=5&startrow=eGlND&endrow=eGlNE

where the scan range has more rows than the limit, the
rest server will start leaking memmory.

Signed-off-by: Andrew Purtell <apurtell@apache.org>

hbase-rest/src/main/java/org/apache/hadoop/hbase/rest/TableScanResource.java

@@ -98,6 +98,9 @@ public class TableScanResource  extends ResourceBase {
                   kv.getTimestamp(), CellUtil.cloneValue(kv)));
             }
             count--;
+            if (count == 0) {
+              results.close();
+            }
             return rModel;
           }
         };