buffet: Allow passing verbosity level to buffet.

Example:

  restart buffet V=2

BUG=None
TEST=Restarted the service manually.

Change-Id: I003a9518bee14a98a06de7c6f96b82cd99c85383
Reviewed-on: https://chromium-review.googlesource.com/220540
Tested-by: Anton Muhin <antonm@chromium.org>
Commit-Queue: Anton Muhin <antonm@chromium.org>
Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>

buffet/etc/init/buffet.conf

diff --git a/buffet/etc/init/buffet.conf b/buffet/etc/init/buffet.conf
index 66cd9ed..6965b7c 100644
--- a/buffet/etc/init/buffet.conf
+++ b/buffet/etc/init/buffet.conf
@@ -13,4 +13,4 @@
   mkdir -p /var/lib/buffet
 end script
 
-exec buffet
+exec buffet --v="${V:-1}"