Deleting a non-existent key through s3api's delete-objects should return a valid response..

```
aws s3api delete-objects --bucket my-bucket --delete '{\"Objects\":[{\"Key\":\"my-key\"}]}'
```
Gives...
```
{
    "Deleted": [
        {
            "Key": "my-key"
        }
    ]
}
```

Deleting a non-existent key through s3api's delete-objects on LocalStack returns an error response without any additional information beyond the key.

```
aws s3api delete-objects --bucket my-bucket --delete '{"Objects":[{"Key":"my-key"}]}' --endpoint-url http://localhost:4572
```
Gives...
```
{
    "ResponseMetadata": {
        "HTTPStatusCode": 200,
        "HTTPHeaders": {
            "server": "BaseHTTP/0.6 Python/3.7.5",
            "date": "Fri, 20 Dec 2019 16:02:39 GMT",
            "content-type": "application/xml; charset=utf-8",
            "content-length": "180",
            "access-control-allow-origin": "*",
            "last-modified": "Fri, 20 Dec 2019 16:02:39 GMT",
            "access-control-allow-methods": "HEAD,GET,PUT,POST,DELETE,OPTIONS,PATCH",
            "access-control-allow-headers": "authorization,content-type,content-md5,cache-control,x-amz-content-sha256,x-amz-date,x-amz-security-token,x-amz-user-agent,x-amz-target,x-amz-acl,x-amz-version-id,x-localstack-target,x-amz-tagging",
            "access-control-expose-headers": "x-amz-version-id"
        },
        "RetryAttempts": 0
    },
    "Errors": [
        {
            "Key": "my-key"
        }
    ]
}
```

Deleting an existent key seems to work fine.
parsed = urlparse.urlparse(path)
    path_parts = parsed.path.lstrip('/').split('/', 1)
    if uses_path_addressing(headers):
        return path_parts[1]
    return path_parts[0]
def uses_path_addressing(headers):
    host = headers['host']
    return host.startswith(HOSTNAME) or host.startswith(HOSTNAME_EXTERNAL)
def get_bucket_name(path, headers):
    parsed = urlparse.urlparse(path)
    
    bucket_name = parsed.path.split('/')[1]
    
    if uses_path_addressing(headers):
        return normalize_bucket_name(bucket_name)
    
    
    
    common_pattern = re.compile(r'^(.+)\.s3[.\-][a-z]{2}-[a-z]+-[0-9]{1,}'
                                r'\.amazonaws\.com(\.[a-z]+)?$')
    
    
    
    dualstack_pattern = re.compile(r'^(.+)\.s3\.dualstack\.[a-z]{2}-[a-z]+-[0-9]{1,}'
                                   r'\.amazonaws\.com(\.[a-z]+)?$')
    
    
    
    legacy_patterns = re.compile(r'^(.+)\.s3\.?(-external-1)?\.amazonaws\.com(\.[a-z]+)?$')