[compute] Networks array suffers from chef attribute level merging

[Joseph Rafferty]

When I specify an array of networks in an environment's default_attributes, those networks are set-unboned with the networks from the cookbook's default attributes.

If I change my environment to specify networks in override_attributes, I lose the ability the override any attributes at a node-level.

I'd like to propose changing the network attribute to be a hash rather than array, with the key being the network label. Like what is documented in README.md for the two default networks ("public" and "private").

For instance,

"default_attributes": {
  "openstack": {
    "compute": {
      "networks": {
        "public": {
           attrs...
        },
        "private": {
           attrs...
        },
        "othernet": {
          attrs...
        }
      }
    }
  }
}

This would allow one to completely override the networks at a default level in an environment or role, while still being able to override at a node level with deep-merge using normal attributes.

Changes in the nova-setup recipe will need to reflect supporting a Hash, and should be able to continue supporting an array relatively simply to prevent a breaking change.