fix reconnects of auth_user dbs after online restart

if the user was a dynamic user, the only way the bouncer knows the
password was from a new client connection. if an existing client
starts a transaction before a new client connects, it will not know
the correct password. so pass that info along in the online restart
data.

note that this is backwards compatible - old bouncers just won't send
the password, and it's stuck until the client tries to connect