[spark] Show livy session process logs

curl localhost:8998/sessions/0 | python -m json.tool
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   196    0   196    0     0  13927      0 --:--:-- --:--:-- --:--:-- 14000
{
    "id": 0,
    "kind": "spark",
    "log": [
        "Invalid initial heap size: -Xms1mb",
        "Error: Could not create the Java Virtual Machine.",
        "Error: A fatal exception has occurred. Program will exit."
    ],
    "state": "error"
}