always exit on xbmc.abortRequested

Smaskis in irc reported that he has reboot issues. after quick investigation we found that it's caused by our service addon, seems a bug introduced in 28b35c8

here is a log: http://sprunge.us/UCbP

the issue happens ONLY if first invocation of check_updates_v2 (right after boot) fails, which, anyway, should not be called if update is set to "manual" as in his case (that's another issue you have to look at)

this patch is confirmed to work. it does not fix the root cause of the issue, but I'd recommend merging anyway, as we can't manualy stop the addon (start="startup") - it should always exit on reboot / shutdown, zero delay is a must