buffet: Merge registration start and finalization.

As currently user-initiated registration flow is recommended,
it allows us to simplify registration protocol to a single method.

BUG=None
TEST=cros_workon_make buffet --test && manual testing.

Change-Id: I1937b91f4f7b34585ce5b8cb1a4c26ec3a849865
Reviewed-on: https://chromium-review.googlesource.com/223700
Commit-Queue: Anton Muhin <antonm@chromium.org>
Tested-by: Anton Muhin <antonm@chromium.org>
Reviewed-by: Anton Muhin <antonm@chromium.org>
8 files changed
tree: 53c0eb8b1dbac10aa735fe1ada4d0d865d9ab92e
  1. buffet/