Add last_scheduling_status to JSON output for VMs, clusters, and networks

[divolgin]

Adds additional status info:

$ replicated vm ls -o json | jq '.[] | {id: .id, status: .status, last_scheduling_status: .last_scheduling_status}'
{
  "id": "0ded16aa",
  "status": "queued",
  "last_scheduling_status": "exceeds-limits"
}
{
  "id": "fcc76736",
  "status": "running",
  "last_scheduling_status": ""
}
{
  "id": "7c663f0f",
  "status": "queued",
  "last_scheduling_status": "exceeds-limits"
}
{
  "id": "dd2351b0",
  "status": "queued",
  "last_scheduling_status": "exceeds-limits"
}