### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

Currently the VTL template for `request_templates` is not processed properly:

```
#set( $body = $input.json("$") )

#macro( loop $map )
{
    #foreach($key in $map.keySet())
        #set( $k = $util.escapeJavaScript($key) )
        #set( $v = $util.escapeJavaScript($map.get($key)).replaceAll("\\'", "'") )
        "$k": "$v"
        #if( $foreach.hasNext ) , #end
    #end
}
#end

{
    "enhancedAuthContext": #loop($context.authorizer),

    "headers": #loop($input.params().header),

    "query": #loop($input.params().querystring),

    "path": #loop($input.params().path),

    "identity": #loop($context.identity),

    "stageVariables": #loop($stageVariables),
}
EOF
}
```

results in,

```
'

{
    "enhancedAuthContext": {
    }
,

    "headers": {
    }
,

    "query": {
    }
,

    "path": {
    }
,

    "identity": {
    }
,

    "stageVariables": {
    }
,
}
'
```

### Expected Behavior

The template should be rendered and have the JSON properties.

### How are you starting LocalStack?

Custom (please describe below)

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

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

    awslocal s3 mb s3://mybucket


### Environment

```markdown
- OS: MacOS
- LocalStack: 0.14
```


### Anything else?

This example can be used to validate.
https://github.com/localstack/localstack-terraform-samples/tree/master/apigateway-lambda-velocity
return firehose_arn.split("/")[-1]
def kinesis_stream_name(kinesis_arn):
    return kinesis_arn.split(":stream/")[-1]
def mock_aws_request_headers(service="dynamodb", region_name=None, access_key=None):
    ctype = APPLICATION_AMZ_JSON_1_0
    if service == "kinesis":
        ctype = APPLICATION_AMZ_JSON_1_1
    elif service in ["sns", "sqs"]:
        ctype = APPLICATION_X_WWW_FORM_URLENCODED
    
    access_key = access_key or constants.TEST_AWS_ACCESS_KEY_ID
    region_name = region_name or get_region()
    headers = {
        "Content-Type": ctype,
        "Accept-Encoding": "identity",
        "X-Amz-Date": "20160623T103251Z",
        "Authorization": (
            "AWS4-HMAC-SHA256 "
            + "Credential=%s/20160623/%s/%s/aws4_request, "
            + "SignedHeaders=content-type;host;x-amz-date;x-amz-target, Signature=1234"
        )
        % (access_key, region_name, service),
    }
    return headers
def inject_region_into_auth_headers(region, headers):