This change focus to provide a framework to define and deploy policies,
and focus to integrate Salt and Vault.

The Salt primary server has a salt_primary policy to be able
to generate token with specific policies for other nodes.

Nodes receive policy for the exact paths of credentials they need,
as the ops/secrets/ namespace is shared between Salt deployment
and application own needs.

Ref T928, T1425

vault policy list

salt-call vault.read_secret on various nodes, to check they can access theirs
but not others. Salt correctly log in with a permission allowing to create more
tokens with salt-node-* policy, and assign the correct one to each node.