replication: interrupt failover if the main device is closed

Without this change, there is a race condition in tests/test-replication.
Depending on how fast the failover job (active commit) runs, there is a
chance of two bad things happening:

1) replication_done can be called after the secondary has been closed
and hence when the BDRVReplicationState is not valid anymore.

2) two copies of the active disk are present during the
/replication/secondary/stop test (that test runs immediately after
/replication/secondary/start, which tests failover).  This causes the
corruption detector to fire.
Reviewed-by: NWen Congyang <wency@cn.fujitsu.com>
Reviewed-by: NChanglong Xie <xiecl.fnst@cn.fujitsu.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NFam Zheng <famz@redhat.com>
Message-Id: <1477565348-5458-2-git-send-email-pbonzini@redhat.com>
Signed-off-by: NFam Zheng <famz@redhat.com>

block/replication.c

@@ -138,6 +138,9 @@ static void replication_close(BlockDriverState *bs)
     if (s->replication_state == BLOCK_REPLICATION_RUNNING) {
         replication_stop(s->rs, false, NULL);
     }
+    if (s->replication_state == BLOCK_REPLICATION_FAILOVER) {
+        block_job_cancel_sync(s->active_disk->bs->job);
+    }
 
     if (s->mode == REPLICATION_MODE_SECONDARY) {
         g_free(s->top_id);