GitLab

Now users are blocked on online signin when authpolicyd failed to get
kerberos credentials

BUG=chromium:824204
TEST=AuthPolicyCredentialsManagerTest.*

Change-Id: Iae490a5615842aaae356e29501667453d86cd11c
Reviewed-on: https://chromium-review.googlesource.com/983917
Commit-Queue: Roman Sorokin <rsorokin@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547687}