fixed ex/ex_id/slicer api endpoint error resolves #660

[jsnoble]

After testing it seemed that the endpoint works correctly. I got the error reported only when I used the job_id instead of the ex_id for that endpoint. Take note that you can call /jobs/:job_id/slicer with the job_id that is returned assuming you only have one invocation, if you dont you will just get multiple back. If you call /ex/:ex_id/slicer it must be with an actual ex_id, which you would have to dig around a bit. The error was not reporting back correctly so I fixed that

[kstaken]

Manually verified.

curl localhost:5678/jobs/3299b2ea-2a56-45ba-85f5-a5ea5df5f798/slicer
[
    {
        "ex_id": "7238d2a3-4cd1-4a1f-b4df-14a80ab8f3d7",
        "job_id": "3299b2ea-2a56-45ba-85f5-a5ea5df5f798",
        "name": "Data Generator",
        "workers_available": 0,
        "workers_active": 1,
        "workers_joined": 1,
        "workers_reconnected": 0,
        "workers_disconnected": 0,
        "failed": 0,
        "subslices": 0,
        "queued": 1,
        "slice_range_expansion": 0,
        "processed": 34,
        "slicers": 1,
        "subslice_by_key": 0,
        "started": "2018-02-14T13:38:01.560-07:00"
    }
]

curl localhost:5678ex/7238d2a3-4cd1-4a1f-b4df-14a80ab8f3d7/slicer
[
    {
        "ex_id": "7238d2a3-4cd1-4a1f-b4df-14a80ab8f3d7",
        "job_id": "3299b2ea-2a56-45ba-85f5-a5ea5df5f798",
        "name": "Data Generator",
        "workers_available": 0,
        "workers_active": 1,
        "workers_joined": 1,
        "workers_reconnected": 0,
        "workers_disconnected": 0,
        "failed": 0,
        "subslices": 0,
        "queued": 1,
        "slice_range_expansion": 0,
        "processed": 40,
        "slicers": 1,
        "subslice_by_key": 0,
        "started": "2018-02-14T13:38:01.560-07:00"
    }
]