Tweak `multi_source.master_info_file` re. MDEV-31857’s new default
`Master_SSL_Verify_Server_Cert=0` was optional before that
secure-by-default change. Now, passwordless connections must disable
SSL certificate verification.
Because the default unnamed connection cannot be deleted by RESET
REPLICA ALL, it must be explicitly left passwordless and having
`Master_SSL_Verify_Server_Cert=0`. The named connection is cleaned
up by RESET REPLICA ALL and thus not affected.
Add MTR tests in the `multi_source` suite to validate future changes
that they does not affect the function of these two `mariadbd` options
```
master_info_file
rpl_show_slave_auth_info
```
Reviewed-by: Susil Kumar Behera <susil.behera@mariadb.com>
