buffet: Properly create buffet directory.

Now when buffet is ran under buffet user, it should be
granted special permissions to be able to write under
/var/lib/buffet.

BUG=None
TEST=manual

Change-Id: I83b0c59c4db54eb6a3a0c9af986b811fe4744f38
Reviewed-on: https://chromium-review.googlesource.com/231333
Tested-by: Anton Muhin <antonm@chromium.org>
Commit-Queue: Anton Muhin <antonm@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>

buffet/etc/init/buffet.conf

diff --git a/buffet/etc/init/buffet.conf b/buffet/etc/init/buffet.conf
index 9e628c5..0d7697e 100644
--- a/buffet/etc/init/buffet.conf
+++ b/buffet/etc/init/buffet.conf
@@ -10,7 +10,8 @@
 respawn
 
 pre-start script
-  mkdir -p /var/lib/buffet
+  mkdir -m 0755 -p /var/lib/buffet
+  chown -R buffet:buffet /var/lib/buffet
 end script
 
 # Minijail actually forks off our desired process.