Add local_auth_info_changed -> root_client_token_owner

We are going to store owner of Root Client Authentication Token.
Information is needed to avoid claiming tokens by multiple clients
or by client and cloud simultaneously.

BUG=26156215

Change-Id: I4dae39f3e8b0cfe3667775a864d5c893710fc18e
Reviewed-on: https://weave-review.googlesource.com/1921
Reviewed-by: Alex Vakulenko <avakulenko@google.com>