Save the client base JID for authentication in case it differs from the email (for accounts non-Google email). Keep a separate email field for use in user-facing UIs, logs, etc. Using the existing host_owner field for the base JID guarantees the correct *functional* behavior (i.e. authentication-wise) if the new config is used with an older host (the only difference is aesthetic - in that older host some UI/logs may show an uglier address instead of the user email).

BUG=224742

Review URL: https://codereview.chromium.org/595063005

Cr-Commit-Position: refs/heads/master@{#297269}