qmp: add block_job_cancel command

Add block_job_cancel, which stops an active block streaming operation.
When the operation has been cancelled the new BLOCK_JOB_CANCELLED event
is emitted.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/qmp-commands.hx b/qmp-commands.hx
index e4615ca..0795c5d 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -661,6 +661,12 @@
     },
 
     {
+        .name       = "block_job_cancel",
+        .args_type  = "device:B",
+        .mhandler.cmd_new = qmp_marshal_input_block_job_cancel,
+    },
+
+    {
         .name       = "blockdev-snapshot-sync",
         .args_type  = "device:B,snapshot-file:s,format:s?",
         .mhandler.cmd_new = qmp_marshal_input_blockdev_snapshot_sync,