power: Suspend instead of shutting down for TPM counter.

Add a tpm_counter_suspend_threshold powerd pref. If the
TPM's dictionary-attack counter reaches this value, idle and
lid-closed "shut down" actions will be overridden to
suspend instead.

Also give the "power" user permission to call cryptohomed's
GetTpmStatus D-Bus methoed.

BUG=chromium:462428
TEST=added unit tests; also manually tested by setting the
     pref and watching /var/log/power_manager/powerd.LATEST
CQ-DEPEND=CL:254570

Change-Id: I3c5944ea5faaf78eedc074a1292f4d8124194d45
Previous-Reviewed-on: https://chromium-review.googlesource.com/254670
(cherry picked from commit 696bd299934f40c706f2ac378a6995336efbbf90)
Reviewed-on: https://chromium-review.googlesource.com/259280
Reviewed-by: Dan Erat <derat@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
Commit-Queue: Luigi Semenzato <semenzato@chromium.org>
Tested-by: Luigi Semenzato <semenzato@chromium.org>
10 files changed