Make asyncio tests run on Windows.

Lib/test/test_asyncio/test_streams.py

 """Tests for streams.py."""
 
 import gc
-import ssl
 import unittest
 import unittest.mock
+try:
+    import ssl
+except ImportError:
+    ssl = None
 
 from asyncio import events
 from asyncio import streams

Lib/test/test_asyncio/test_unix_events.py

@@ -10,6 +10,9 @@ import sys
 import unittest
 import unittest.mock
 
+if sys.platform == 'win32':
+    raise unittest.SkipTest('UNIX only')
+
 
 from asyncio import events
 from asyncio import futures

Lib/test/test_asyncio/test_windows_utils.py

@@ -11,7 +11,11 @@ if sys.platform != 'win32':
 import _winapi
 
 from asyncio import windows_utils
-from asyncio import _overlapped
+
+try:
+    import _overlapped
+except ImportError:
+    from asyncio import _overlapped
 
 
 class WinsocketpairTests(unittest.TestCase):