spice: turn client_migrate_info to async

RHBZ 737921
Spice client is required to connect to the migration target before/as migration
starts. Since after migration starts, the target qemu is blocked and cannot accept new spice client
we trigger the connection to the target upon client_migrate_info command.
client_migrate_info completion cb will be called after spice client has been
connected to the target (or a timeout). See following patches and spice patches.

Signed-off-by: Yonit Halperin <yhalperi@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/qmp-commands.hx b/qmp-commands.hx
index 4328e8b..cb60d0c 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -569,7 +569,8 @@
         .params     = "protocol hostname port tls-port cert-subject",
         .help       = "send migration info to spice/vnc client",
         .user_print = monitor_user_noop,
-        .mhandler.cmd_new = client_migrate_info,
+        .mhandler.cmd_async = client_migrate_info,
+        .flags      = MONITOR_CMD_ASYNC,
     },
 
 SQMP