Support dnspython 2

$ pip install --upgrade dnspython eventlet                                

Requirement already satisfied: dnspython in /Users/shane/pymongo-pycharm-3.8/lib/python3.8/site-packages (2.1.0)

Requirement already satisfied: eventlet in /Users/shane/pymongo-pycharm-3.8/lib/python3.8/site-packages (0.32.0)

Requirement already satisfied: six>=1.10.0 in /Users/shane/pymongo-pycharm-3.8/lib/python3.8/site-packages (from eventlet) (1.15.0)

Requirement already satisfied: greenlet>=0.3 in /Users/shane/pymongo-pycharm-3.8/lib/python3.8/site-packages (from eventlet) (1.0.0)

$  mongo-python-driver git:(master) PYMONGO_MUST_CONNECT=1 python green_framework_test.py eventlet -s test.test_client_context

running test

running egg_info

writing pymongo.egg-info/PKG-INFO

writing dependency_links to pymongo.egg-info/dependency_links.txt

writing requirements to pymongo.egg-info/requires.txt

writing top-level names to pymongo.egg-info/top_level.txt

reading manifest file 'pymongo.egg-info/SOURCES.txt'

reading manifest template 'MANIFEST.in'

writing manifest file 'pymongo.egg-info/SOURCES.txt'

running build_ext

test_enableTestCommands_is_disabled (test.test_client_context.TestClientContext) ... skipped 'PYMONGO_DISABLE_TEST_COMMANDS is not set'

test_must_connect (test.test_client_context.TestClientContext) ... ok

test_serverless (test.test_client_context.TestClientContext) ... skipped 'TEST_SERVERLESS is not set'

test_setdefaultencoding_worked (test.test_client_context.TestClientContext) ... skipped 'SETDEFAULTENCODING is not set'

----------------------------------------------------------------------

Ran 4 tests in 0.000s

OK (skipped=3)