virsh: Free stream when shutdown console

Otherwise connection of hypervisor driver will be leaked when
one shutdown the guest in console. e.g.

[root@localhost]# init 0
......
init: Re-executing /sbin/init
Halting system...
Power down.

error: Failed to disconnect from the hypervisor, 1 leaked reference(s)

tools/console.c

@@ -92,6 +92,8 @@ virConsoleShutdown(virConsolePtr con)
 {
     con->quit = true;
     virStreamEventRemoveCallback(con->st);
+    if (con->st)
+        virStreamFree(con->st);
     if (con->stdinWatch != -1)
         virEventRemoveHandle(con->stdinWatch);
     if (con->stdinWatch != -1)