DNSPodDNSTests.test_create_record_success() returns an unexpected value

## `DNSPodDNSTests.test_create_record_success()` returns an unexpected value

Consider the following code (in [test_dnspod.py](https://github.com/apache/libcloud/blob/6b588346083a510396c63b5d18db3012aa083071/libcloud/test/dns/test_dnspod.py#L156)):

def test_create_record_success(self):
DNSPodMockHttp.type = 'CREATE_RECORD_SUCCESS'
record = self.driver.create_record(name='@', zone=self.test_zone,
type='A', data='96.126.115.73',
extra={'ttl': 13,
'record_line': 'default'})

## Expected result

I would expect `record.extra['ttl']` to be an int 13

## Actual result

The actual result, when running this unit test is:

`record.extra['ttl']` is the string `'600'`.
`record.ttl` is `None`.

Note that `'600'` (yes, a string) is the default TTL of the `self.test_zone`. [See the explicit check in line 61](https://github.com/apache/libcloud/blob/6b588346083a510396c63b5d18db3012aa083071/libcloud/test/dns/test_dnspod.py#L61).

## Detailed Information

At first, I expected an error in `DNSPodDNSDriver.create_record()`. Perhaps it ignored the `extra` parameter.

However, the `extra` dict is merged in the `data` dict, which is send to the DNSPod API, so that seems correct (although I don't know the intrinsics of the DNSPod API can am not sure).

Diving deeper in the test code, the perhaps likely explanation is that the API simulator (DNSPodMockHttp) returns the incorrect results. `DNSPodMockHttp._Record_Create_CREATE_RECORD_SUCCESS()` is called, which returns the contents of [`get_record.json`](https://github.com/apache/libcloud/blob/trunk/libcloud/test/dns/fixtures/dnspod/get_record.json). That file indeed contains `"ttl": "600",`. So I suspect that the unit test is flawed, not the actual code or DNSPod API (although I can't verify without access to this API).

## Suggested Fix

Without a contributor who has access to this API, my suggested solution is to disable this particular assertion in `DNSPodDNSTests.test_create_record_success()`.

This fix is included in #1537

libcloud/test/dns/test_dnspod.py、特に DNSPodDNSTests.test_create_record_success() から始め、DNSPodMockHttp のレスポンスパスと libcloud/test/dns/fixtures/dnspod/get_record.json を調べてください。対象を絞ったテストを実行し、fixture の TTL とテストで期待されるレコードフィールドを比較してください。assertion と fixture のどちらが API の動作を表すべきかを判断し、issue #1537 で提案されている修正を確認してください。

索引モデルが issue の本文から書いたものです。