status json: list the unhealthy_servers under cluster.data.team_trackers

[ltsampros]

In the team_trackers sections of status json, we output the number of unhealthy servers. We should also be listing them explicitly either by id or ip:port to enable easier debugging:

  "data": {
      "team_trackers":[
         {
             "primary":true,
             "in_flight_bytes":0,
             "unhealthy_servers":0,
             "state":{
                 "healthy":true,
                 "min_replicas_remaining":0,
                 "name":{ // when not limiting
                    "$enum":[
                       "initializing",
                       "missing_data",
                       "healing",
                       "optimizing_team_collections",
                       "healthy_populating_region",
                       "healthy_repartitioning",
                       "healthy_removing_server",
                       "healthy_rebalancing",
                       "healthy"
                    ]
                 },
                 "description":""
             }
         }
      ],
 }