Fix propagating of configdn, configpw, monitordn, monitorpw into

the slapd.conf file.

Using a parameter, as default for another paramter as it is done in the 
server.pp file for above 4 named parameters, is not going to work as intended.
This will basically end up with 4 empty strings that get used in the template file.

Also, be more cautious, when, especially the *pw variables get
written to the file. Further, the suffix= line in the database config
section is not allowed:

Basically fixing error messages like this with enabled config and monitoring
databases:

543e1cc9 /etc/openldap/slapd.conf: line 23: suffix <cn=config> not allowed in config database.
543e1cc9 /etc/openldap/slapd.conf: line 23: <suffix> handler exited with 1!

with rootpw under database config
543e1d10 line 25 (rootpw ***)
543e1d10 /etc/openldap/slapd.conf: line 25: <rootpw> can only be set when rootdn is under suffix

with rootpw under database monitor
543e1dc6 line 38 (rootpw ***)
543e1dc6 /etc/openldap/slapd.conf: line 38: <rootpw> can only be set when rootdn is under suffix

For that last reason, the suffix= line in the config database
is commented out, as it is done for the monitor database already.

Unfortunately the setting of the parameters seems a bit confusing, but since puppet doesn't allow
re-assigning of variables, I had to work around it. 

my tests are done with openldap-2.4.40, and without explicitly setting a configdn or monitordn, because I want to have the same as the rootdn. But at least my changes make this now work for me having a config and monitoring database backend.


If the documentation for those params states that they are automatically inherited from the rootdn if not set, then we should ensure the same behaviour, i.e.

```
$configdn  = undef,
$configpw  = undef,
$monitordn = undef,
$monitorpw = undef,
```

The templates should then only attempt to set these params if they're not undef.. there shouldn't be any need for additional logic in the server.pp