Add Kerberos client

Adds a real and a fake implementation of a D-Bus client that talks to
the Kerberos daemon in Chrome OS.

BUG=chromium:933798
TEST=Validated the fake and real implementation with custom test code

Change-Id: Ic4f025c87ed17f242c383c42d00972e9c5606c4a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1478895
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Lutz Justen <ljusten@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641758}
7 files changed