ctr: fix parsing mount options

Set 'DisableSliceFlagSeparator = true'

urfave/cli/v2 uses ',' as default string slice separator.
That means '--mount type=bind,src=/src,des=/des,options=rbind:rw'
will be token as four bind mount options.

Fixes: containerd#10003

Signed-off-by: baijia <baijia.wr@antgroup.com>

Author: baijia

cmd/ctr/app/main.go

@@ -86,6 +86,7 @@ stable from release to release of the containerd project.`
 
 containerd CLI
 `
+	app.DisableSliceFlagSeparator = true
 	app.EnableBashCompletion = true
 	app.Flags = []cli.Flag{
 		&cli.BoolFlag{