Bug: 'NoSuchBucket' Exception is thrown when an object doesn't exists.

[krwu]

When you try to retrieve a non-exist object from an exists bucket, It should throw NoSuchKeyException, not NoSuchBucketException.

Test code:

$client = new Client(array(
    'region' => 'gz',
    'credentials' => array(
        'appId' => '{appId}',
        'secretId' => '{secretId}',
        'secretKey' => '{secretKey}'
    )
));

try {
    $result = $client->headObject(array(
        'Bucket' => '{exists bucket}',
        'Key' => '{non-exists key}'
    ));
    print_r($result);
} catch ( NoSuchKeyException $e ) {
    echo 'No such key.';
} catch ( NoSuchBucketException $e) {
    echo 'No such bucket.';
}

The output will be "No such bucket."