qemu-img: add compressed clusters to BlockFragInfo

Show how many clusters are compressed.  This can be used to monitor how
many compressed clusters remain and whether to recompress the image.

Suggested-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/include/block/block.h b/include/block/block.h
index ce61883..9661f9a 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -24,6 +24,7 @@
     uint64_t allocated_clusters;
     uint64_t total_clusters;
     uint64_t fragmented_clusters;
+    uint64_t compressed_clusters;
 } BlockFragInfo;
 
 typedef struct QEMUSnapshotInfo {