Add master candidates IPs informations to ssconf

This will be used when querying confd, in order not to rely on DNS being
available.

Signed-off-by: Luca Bigliardi <shammash@google.com>
Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>