fix verbose error message thrown by invalid enum

[ylwu-amzn]

Signed-off-by: Yaliang Wu ylwu@amazon.com

Description

1. Don't return verbose error message when use input invalid enum.
2. Fix some code style

Test:

POST /_plugins/_ml/_train/kmeans
{
    "parameters": {
        "k": 2,
        "iterations": 10,
        "distance_type": "SINE"
    },
    "input_query": {
        "query": {
            "bool": {
                "filter": [
                    {
                        "range": {
                            "k1": {
                                "gte": 0
                            }
                        }
                    }
                ]
            }
        },
        "size": 10
    },
    "input_index": [
        "test_data"
    ]
}

# Response
{
    "error": {
        "root_cause": [
            {
                "type": "illegal_argument_exception",
                "reason": "Wrong distance type"
            }
        ],
        "type": "illegal_argument_exception",
        "reason": "Wrong distance type"
    },
    "status": 400
}

Issues Resolved

Close #163

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[Zhangxunmt]

lgtm