[luciexe] Fix auth_test.go.
[luciexe] Fix auth_test.go.

It broke on non-GCE after
https://chromium.googlesource.com/infra/luci/luci-go/+/2c85aa6f9b3628

R=yiwzhang@google.com

Change-Id: I59d4d1e943349e27b70ab7c3bb4a171b51f38a9f
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/3069752
Reviewed-by: Scott Lee <1dcb292530f82960316cb3d87cd67c3f212b79cb@chromium.org>
Commit-Queue: Vadim Shtayura <9f116ddb1b24f6fc1916a676eb17161b6c07dfc1@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go