Boaz Leskes 5ac7bd83ad Expose min/max open file descriptors in Cluster Stats API
Also changes the response format of that section to:

```
 "open_file_descriptors": {
      "min": 200,
      "max": 346,
       "avg": 273
 }
```

Closes #4681

Note: this is an aggregate of 3 commits in the 0.90 branch
2014-01-10 12:15:56 +01:00
..
2014-01-06 08:33:32 +01:00