Rudder

Today, we are deleting the inventory file after sending it to the node's promises server. There is no good reason for that safe saving space, and a lot of reason to keep the N last inventories on the node, for example:

- debugging
- using the file for other things than Rudder
- being able to see when the last inventory was generated on a node
- etc

So we should at least keep the last inventory file on the node in a standardised place, and perhaps even the N last.

Perhaps we have to keep a configuration option somewhere to force not keep the inventory file in extremelly space constrained environment (but we are talking of less than 1Mo, more likelly 50ko-200ko, especially on constrained device with little softwares, processes).