Rudder

We want to add system group / directive / rules for DSC agent, but also to not apply CFEngine system rules to these nodes.

The group case is funny.
We have two cases for CFEngine technique applied to lots of node today for special target:

- special:all : that target is used by "inventory" directive. It must be changed toward a rule applying to "all CFEngine agent" (because we want to keep the semantic of "special:all" to actually all nodes)
- special:hasPolicyServer:(root, relay-uuid): that one is used in fact only for CFEngine nodes. We need to renamed it (not in the serialized part for compatibility reason, but at least in the code) to CFEAgentWithPolicyServer and limit its reached in the code.

The second one is actually implemented as a dynamic group (not a special target), so we must add the possibility to target all cfengine nodes by a mean or an other).

We will need to also change the bootstrap ldif for "common" rule and change the target, and add a migration to also change it in 4.1 -> 4.2 (it could also be done when installing the DSC plugin but it seems a worse place to do it)