Rudder

At several part in the code, we need to know what is the kind of node we are dealing with, with generally a special cases for the root server.

For now, the detection of the type of node is done in an ad-hoc way (by checking if the policy server id of the node is the same as the node itself).

With the addition of role, we can have a far better way to know that, and a more precise one.

For example, today, we have two LDAP tructural types of node entries: rudderNode and rudderPolicyServer (sup: rudderNode). This is an heritage of a time where a rudderPolicyServer had special, dedicated attributes. It is no more the case, and we don't use that AT all (because at the scala level, we don't keep that information in that way).

I'm not sur if this is mandatory for now, or if it is part of more global cleaning with no direct user visible effect (appart from "less bug and more feature in the long run"). If it is not mandatory, I propose to post-pone that for 2.12 so that we can see all the implication of the server role add.