tests/extmod: Add very basic feature test for ussl module.

This test just tests that the basic functions/methods can be called with
the appropriate arguments.  There is no real test of underlying
functionality.

Thanks to @hosaka for the initial implementation of this test.

tests/extmod/ussl_basic.py

+# very basic test of ssl module, just to test the methods exist
+
+try:
+    import uio as io
+    import ussl as ssl
+except ImportError:
+    print("SKIP")
+    import sys
+    sys.exit()
+
+# create in client mode
+try:
+    ss = ssl.wrap_socket(io.BytesIO())
+except OSError as er:
+    print('wrap_socket:', repr(er))
+
+# create in server mode (can use this object for further tests)
+socket = io.BytesIO()
+ss = ssl.wrap_socket(socket, server_side=1)
+
+# print
+print(repr(ss)[:12])
+
+# setblocking
+try:
+    ss.setblocking(False)
+except NotImplementedError:
+    print('setblocking: NotImplementedError')
+ss.setblocking(True)
+
+# write
+print(ss.write(b'aaaa'))
+
+# read (underlying socket has no data)
+print(ss.read(8))
+
+# read (underlying socket has data, but it's bad data)
+socket.write(b'aaaaaaaaaaaaaaaa')
+socket.seek(0)
+try:
+    ss.read(8)
+except OSError as er:
+    print('read:', repr(er))
+
+# close
+ss.close()
+
+# write on closed socket
+try:
+    ss.write(b'aaaa')
+except OSError as er:
+    print('write:', repr(er))

tests/extmod/ussl_basic.py.exp

+ssl_handshake_status: -256
+wrap_socket: OSError(5,)
+<_SSLSocket 
+setblocking: NotImplementedError
+4
+b''
+read: OSError(-261,)
+write: OSError(-256,)