Rudder

We want to be able to install different Rudder server part on different machine.

This is a the meta-ticket above #4654, that overlook all the part (packaging, but also inventory update, web-app new information to display, updates on system techniques, etc).

For now, we identified at least 4 parts for the server:

- the main Rudder web application (with user interface)
- the application that handles inventories and store them in our LDAP backend
- the LDAP backend
- the postgres backend

There is also the old "relay server" role.

So, we decided to add a "role" attribute on a node description. It will be a list of all the roles the node has.

Roles will be know based on the presence of file in /opt/rudder/etc/server-roles.d
The will be added in node's inventory in the <RUDDER><SERVER_ROLES><SERVER_ROLE> tag.
The then will be available in a node attribute as a list (serverRoles).

An empty list of server roles means that we are dealing with a simple node.