Update test to verify that user 'power' now belongs to 'buffet' user group

BUG=brillo:806
TEST=./build_packages && ./build_image, manual test on device
     test_that -b link --fast 100.96.48.244 security_AccountsBaseline
CQ-DEPEND=CL:265558,CL:265533

Change-Id: Ia9dc78d47e598873c30f4100fd5853242ccc284f
Reviewed-on: https://chromium-review.googlesource.com/265571
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/profiles/base/accounts/group/buffet b/profiles/base/accounts/group/buffet
index 0e6b7a7..c4748e0 100644
--- a/profiles/base/accounts/group/buffet
+++ b/profiles/base/accounts/group/buffet
@@ -1,3 +1,3 @@
 group:buffet
 gid:264
-users:chronos,buffet,privetd
+users:chronos,buffet,privetd,power