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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description

I'm using `localstack:latest` as a docker image. But when I try to create a new Elasticsearch domain with a specific configuration, the `InstanceType` and `InstanceCount` are ignored.

## Expected behavior

`InstanceCount` and `InstanceType` are recognised.

## Actual behavior

InstanceCount and InstanceType are ignored.

# Steps to reproduce

Setup `localstack:latest` as a docker image and try to setup an elasticsearch domain with `--elasticsearch-cluster-config` included.

## Command used to start LocalStack

Since I'm using docker (or more specific docker-compose) I'm using `docker-compose up -d`

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)

I've tried 2 different approaches, once with shorthand syntax and one with json syntax, both got the same unexpected Output:

```sh
aws --endpoint-url=http://localhost:4566 es create-elasticsearch-domain --domain-name mylogs-2 --elasticsearch-version 7.10 --elasticsearch-cluster-config '{ "InstanceType": "m3.xlarge.elasticsearch", "InstanceCount": 4, "DedicatedMasterEnabled": true, "ZoneAwarenessEnabled": true, "DedicatedMasterType": "m3.xlarge.elasticsearch", "DedicatedMasterCount": 3}'
```

I'm expecting to get `m3.xlarge.elasticsearch` as `InstanceType` and 4 as `InstanceCount` but the output looks like this:

```json
{
    "DomainStatus": {
        "DomainId": "000000000000/mylogs-2",
        "DomainName": "mylogs-2",
        "ARN": "arn:aws:es:us-east-1:000000000000:domain/mylogs-2",
        "Created": true,
        "Deleted": false,
        "Endpoint": "http://localhost:4571",
        "Processing": false,
        "ElasticsearchVersion": "7.10",
        "ElasticsearchClusterConfig": {
            "InstanceType": "m3.medium.elasticsearch",
            "InstanceCount": 1,
            "DedicatedMasterEnabled": true,
            "ZoneAwarenessEnabled": false,
            "DedicatedMasterType": "m3.medium.elasticsearch",
            "DedicatedMasterCount": 1
        },
        "EBSOptions": {
            "EBSEnabled": true,
            "VolumeType": "gp2",
            "VolumeSize": 10,
            "Iops": 0
        },
        "CognitoOptions": {
            "Enabled": false
        }
    }
}
```

What I get is `m3.medium.elasticsearch` as `InstanceType` instead of `m3.xlarge.elasticsearch`  and 1 as `InstanceCount` instead of 4.

I've used the json syntax as well:
```sh
aws es create-elasticsearch-domain --domain-name mylogs-1 --elasticsearch-version 7.10 --elasticsearch-cluster-config InstanceType=r6g.large.elasticsearch,InstanceCount=6 --endpoint-url=http://localhost:4566
```

but got the same result. :/
@classmethod
    def setUpClass(cls):
        cls.es_url = aws_stack.get_local_service_url('elasticsearch')
        
        cls._create_domain()
        document = {
            'first_name': 'Jane',
            'last_name': 'Smith',
            'age': 32,
            'about': 'I like to collect rock albums',
            'interests': ['music']
        }
        resp = cls._add_document(TEST_DOC_ID, document)
        assert_equal(resp.status_code, 201, msg='Request failed({}): {}'.format(resp.status_code, resp.text))
    @classmethod
    def tearDownClass(cls):
        cls._delete_document(TEST_DOC_ID)
        
        es_client = aws_stack.connect_to_service('es')
        es_client.delete_elasticsearch_domain(DomainName=TEST_DOMAIN_NAME)
        assert_not_in(TEST_DOMAIN_NAME, [d['DomainName'] for d in es_client.list_domain_names()['DomainNames']])
    def test_domain_es_version(self):