Bugfix: 'module' object has no attribute 'UnsupportedExtension'

Bugfix: 'module' object has no attribute 'UnsupportedExtension'

JIRA: YARDSTICK-1100

This Error occur when run kuberntes test case:
The Key is the pyopenssl dependency, it seems
YARDSTICK-1032(https://jira.opnfv.org/browse/YARDSTICK-1032) encounter
the same problem. Downgrade requests from 2.18.2 to 2.11.1 would solve
this problem.

Here it is the error log:
Traceback (most recent call last):
    File "/usr/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
        func(*targs, **kargs)
        File
    "/home/opnfv/repos/yardstick/yardstick/benchmark/core/task.py",
        line 301, in atexit_handler
        context.undeploy()
        File
        "/home/opnfv/repos/yardstick/yardstick/benchmark/contexts/kubernetes.py",
        line 63, in undeploy
        self._delete_ssh_key()
        File
        "/home/opnfv/repos/yardstick/yardstick/benchmark/contexts/kubernetes.py",
        line 133, in _delete_ssh_key
        k8s_utils.delete_config_map(self.ssh_key)
        File
        "/home/opnfv/repos/yardstick/yardstick/common/kubernetes_utils.py",
        line 179, in delete_config_map
        **kwargs)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/apis/core_v1_api.py",
        line 9059, in delete_namespaced_config_map
        (data) =
    self.delete_namespaced_config_map_with_http_info(name,
                        namespace, body, **kwargs)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/apis/core_v1_api.py",
        line 9159, in delete_namespaced_config_map_with_http_info
        collection_formats=collection_formats)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/api_client.py",
        line 321, in call_api
        _return_http_data_only, collection_formats,
        _preload_content,
            _request_timeout)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/api_client.py",
        line 155, in __call_api
        _request_timeout=_request_timeout)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/api_client.py",
        line 387, in request
        body=body)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/rest.py",
        line 256, in DELETE
        body=body)
        File
        "/usr/local/lib/python2.7/dist-packages/kubernetes/client/rest.py",
        line 166, in request
        headers=headers)
        File
    "/usr/local/lib/python2.7/dist-packages/urllib3/request.py",
        line 66, in request
        **urlopen_kw)
        File
    "/usr/local/lib/python2.7/dist-packages/urllib3/request.py",
        line 87, in request_encode_url
        return self.urlopen(method, url, **extra_kw)
        File
        "/usr/local/lib/python2.7/dist-packages/urllib3/poolmanager.py",
        line 321, in urlopen
        response = conn.urlopen(method, u.request_uri, **kw)
        File
        "/usr/local/lib/python2.7/dist-packages/urllib3/connectionpool.py",
        line 601, in urlopen
        chunked=chunked)
        File
        "/usr/local/lib/python2.7/dist-packages/urllib3/connectionpool.py",
        line 346, in _make_request
        self._validate_conn(conn)
        File
        "/usr/local/lib/python2.7/dist-packages/urllib3/connectionpool.py",
        line 850, in _validate_conn
        conn.connect()
        File
    "/usr/local/lib/python2.7/dist-packages/urllib3/connection.py",
        line 337, in connect
        cert = self.sock.getpeercert()
        File
        "/usr/local/lib/python2.7/dist-packages/urllib3/contrib/pyopenssl.py",
        line 348, in getpeercert
        'subjectAltName': get_subj_alt_name(x509)
        File
        "/usr/local/lib/python2.7/dist-packages/urllib3/contrib/pyopenssl.py",
        line 202, in get_subj_alt_name
        except (x509.DuplicateExtension, x509.UnsupportedExtension,
                AttributeError: 'module' object has no attribute 'UnsupportedExtension'

Change-Id: I444dde829c91defb475e045aea094d74fc43e75b
Signed-off-by: chenjiankun <chenjiankun1@huawei.com>