New get Pod logs API

[Binyang2014]

Add new API to get pod logs:
GET /jobs/{job-name}/pods/{podUid}/logs
RESP:

{
   "locations": [
      {"name": "stdout", "uri": "https://nodeIP/podUid/stdout.0?token=string"},
      {"name": "stderr"," uri": "https://nodeIP/podUid/stderr?token=string"}  
   ]
}

[coveralls]

Coverage decreased (-0.1%) to 34.103% when pulling ffc4ff8 on binyli/log-rest into acbec7b on master.