buffet: Use 'gdbus wait' in post-start stanza of Upstart job.

This should fix the race with 'restart buffet' exiting before buffet
claims its D-Bus name.

BUG=brillo:641
TEST=Ran buffet_Registration 100 times without seeing D-Bus errors.
CQ-DEPEND=CL:262610

Change-Id: I01bf94c90a533e3e396fbb9131b7377e72f217e0
Reviewed-on: https://chromium-review.googlesource.com/262620
Trybot-Ready: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
1 file changed
tree: 1c44e00bfaa4aa2f51b50d257e78616086149e36
  1. buffet/