Make /topics/<>/consumers output easier to read

[horkhe]

At the moment the output of GET /topics/<>/consumers looks like this:

"test-group": {
    "pixy_host1_1846_2015-10-28T07:45:04Z": [
      0,
      1,
      2,
      3,
      4,
      5
    ],
    "pixy_host2_1799_2015-10-28T07:18:42Z": [
      6,
      7,
      8,
      9,
      10,
      11
    ],
    "pixy_host3_1883_2015-10-28T04:17:35Z": [
      12,
      13,
      14,
      15,
      16,
      17
    ]
}

It would be easier to digest if all partitions were listed on the same line, e.g.:

"test-group": {
    "pixy_host1_1846_2015-10-28T07:45:04Z": [0,1,2,3,4,5],
    "pixy_host2_1799_2015-10-28T07:18:42Z": [6,7,8,9,10,11],
    "pixy_host3_1883_2015-10-28T04:17:35Z": [12,13,14,15,16,17]
}

[horkhe]

Implemented in e8cc1c3