Add TPMForceUpdateSRKVulnerable.UserAcknowledgment

This CL adds the TPM force update logic with user aknowledgment for the
device wide policy TPMForceUpdateSRKVulnerable introduced in CL:1469462.

Bug: 875266
Change-Id: I8b25aa5f3218b6754b8439afdf8ec8bd47b53ec3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554495
Commit-Queue: Andreea-Elena Costinas <acostinas@google.com>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Dominic Battré <battre@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649896}