HBASE-13861 Fix UI label for BucketCache free & used bytes.

Signed-off-by: Sean Busbey <busbey@apache.org>

hbase-server/src/main/jamon/org/apache/hadoop/hbase/tmpl/regionserver/BlockCacheTmpl.jamon

@@ -382,8 +382,8 @@ are combined counts. Request count is sum of hits and misses.</p>
     <tr>
         <th>Bucket Offset</th>
         <th>Allocation Size</th>
-        <th>Free Count</th>
-        <th>Used Count</th>
+        <th>Free Bytes</th>
+        <th>Used Bytes</th>
     </tr>
 <%for Bucket bucket: buckets %>
     <tr>