The peer login expiration ACL check introduced in #714
filters out peers that are expired and agents receive a network map
without that expired peers.
However, the agents should see those peers in status "Disconnected".
This PR extends the Agent <-> Management protocol
by introducing a new field OfflinePeers
that contain expired peers. Agents keep track of those and display
then just in the Status response.
The ConnStatus is a custom type based on iota
like an enum. The problem was nowhere used to the
benefits of this implementation. All ConnStatus
instances has been compared with strings. I
suppose the reason to do it to avoid a circle
dependency. In this commit the separated status
package has been moved to peer package.
Remove unused, exported functions from engine
