cros: Add Attestation enrollment browser test.

cryptohome and CA network communication is mocked.

Also fixes waiting for js ready in OOBE - it waits for assets
loading.
Also fixes certificate_based_register handling in
policy_testserver.py

Bug: 934224, 912704
Change-Id: Ic5816376e218436c6a2595759fa1bc9dd1b730ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1523099
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Commit-Queue: Roman Sorokin [CET] <rsorokin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641822}
8 files changed