round timing bug

On some firmware versions (e.g. 1.90), the storage device may not show up
in the repository immediately after receiving the notification message.
Add a small polling loop to make sure we don't miss it.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>
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