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_inet/tls_text_errors.py

@@ -1,13 +1,17 @@
 # test that modtls produces a text error message
 
-import socket, ssl, sys
+import socket, ssl
 
 
 def test(addr):
     s = socket.socket()
     s.connect(addr)
     try:
-        s = ssl.wrap_socket(s)
+        ssl_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
+        if hasattr(ssl_context, "check_hostname"):
+            # Disable hostname check on CPython.
+            ssl_context.check_hostname = False
+        s = ssl_context.wrap_socket(s)
         print("wrap: no exception")
     except OSError as e:
         # mbedtls produces "mbedtls -0x7200: SSL - An invalid SSL record was received"