buffet: fix the unit test.

Fix the unit test. refresh Access Token does not generate
Invalid Credentials any more.

BUG=b:38308727
TEST=unit test.

Change-Id: Ibac59cfdc203f1dd92f9371ede2742503d12b021
Reviewed-on: https://weave-review.googlesource.com/10010
Reviewed-by: Kan Yan <kyan@google.com>
1 file changed