tests: Update SSL network tests to use SSLContext, and work on CPython.

Changes are:
- use ssl.SSLContext.wrap_socket instead of ssl.wrap_socket
- disable check_hostname and call load_default_certs() where appropriate,
  to get CPython to run the tests correctly
- pass socket.AF_INET to getaddrinfo and socket.socket(), to force IPv4
- change tests to use github.com instead of google.com, because certificate
  validation was failing with google.com

Signed-off-by: Damien George <damien@micropython.org>

tests/net_hosted/connect_nonblock_xfer.py

@@ -27,11 +27,12 @@ def do_connect(peer_addr, tls, handshake):
             print("  got", er.errno)
     # wrap with ssl/tls if desired
     if tls:
+        ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+        if hasattr(ssl_context, "check_hostname"):
+            ssl_context.check_hostname = False
+
         try:
-            if sys.implementation.name == "micropython":
-                s = ssl.wrap_socket(s, do_handshake=handshake)
-            else:
-                s = ssl.wrap_socket(s, do_handshake_on_connect=handshake)
+            s = ssl_context.wrap_socket(s, do_handshake_on_connect=handshake)
             print("wrap: True")
         except Exception as e:
             dp(e)