Do not set preferred email until after registration

Gerrit should never set the preferred email unless the address has
been verified by the authentication system (e.g. LDAP importing it)
or the user has confirmed the address by following the verification
link in the email Gerrit sent.

Change-Id: Ie2a4834547175f5f5092dc07b88d30e2a5e2de7b
3 files changed