Only inject certifi certificates on Windows if using TLS

[prashantmital]

Currently, we always end up passing tlsCAFile=certifi.where() on windows which ends up implicitly enabling TLS even if the server is running without it. The error looks like this:

======================================================================
ERROR: test_simple (astrolabe.validator.ValidateWorkloadExecutor)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabe\validator.py", line 45, in setUp
    load_test_data(self.CONNECTION_STRING, DRIVER_WORKLOAD)
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabe\utils.py", line 140, in load_test_data
    coll.drop()
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\collection.py", line 1103, in drop
    dbo.drop_collection(self.__name, session=session)
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\database.py", line 914, in drop_collection
    with self.__client._socket_for_writes(session) as sock_info:
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\mongo_client.py", line 1266, in _socket_for_writes
    server = self._select_server(writable_server_selector, session)
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\mongo_client.py", line 1253, in _select_server
    server = topology.select_server(server_selector)
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\topology.py", line 235, in select_server
    address))
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\topology.py", line 193, in select_servers
    selector, server_timeout, address)
  File "c:\data\mci\8a509a3df3bdd3bf029acf5b0edc5187\astrolabe-src\astrolabevenv\lib\site-packages\pymongo\topology.py", line 209, in _select_servers_loop
    self._error_message(selector))
pymongo.errors.ServerSelectionTimeoutError: SSL handshake failed: localhost:27017: [WinError 10054] An existing connection was forcibly closed by the remote host

Instead, we can use a try...except block to only inject the CA cert file on SSL failures.

[prashantmital]

Caused by #26

[prashantmital]

This is causing EVG failures on Windows with the workload executor validation task - see https://evergreen.mongodb.com/version/5eb26cfb3627e04b03ed0da8.