Add the "deployed_nodes" feature.

once deployed a job (or a role) is associated to its "deployed nodes" list
which can differ from its "assigned_nodes" (or servers) list in case of failure during the deployment.

ADD
 - attribute deployed_nodes to keep track of the deployed nodes for a given job a role.
 - attribute links_deployments to keep track of the links between a job (or role) and a deployment uid.
 - method update_links_deployment, called after a deployment submission to update the links_deployments attribute.
 - method update_deployed_nodes, called after a deployment to update the deployed_nodes attribute.
 - intersect_nodes_[job|role] method to intersect assigned and deployed nodes.
 - get_deployed_nodes to retrieve the deployed of a given job or role.

MODIFY
  - update_cache to cache restfully job property, roles, deployed_nodes and links_deployments
  - add restfully jobs and deployments in self.jobs and self.deployments.

Matt