qcow2: flush in qcow2_update_snapshot_refcount()

Users of qcow2_update_snapshot_refcount() do not flush consistently.
qcow2_snapshot_create() flushes but qcow2_snapshot_goto() and
qcow2_snapshot_delete() do not.

Solve this by moving the bdrv_flush() into
qcow2_update_snapshot_refcount().

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2-refcount.c

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 4d9df5f..3d29d30 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -851,7 +851,7 @@
         }
     }
 
-    ret = 0;
+    ret = bdrv_flush(bs);
 fail:
     if (l2_table) {
         qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table);

block/qcow2-snapshot.c

diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index f4719d9..992a5c8 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -381,11 +381,6 @@
         goto fail;
     }
 
-    ret = bdrv_flush(bs);
-    if (ret < 0) {
-        goto fail;
-    }
-
     /* Append the new snapshot to the snapshot list */
     new_snapshot_list = g_malloc((s->nb_snapshots + 1) * sizeof(QCowSnapshot));
     if (s->snapshots) {