tcpclient: catch any socket() errors

so we can try next addresses, e.g. when trying to connect to IPv6
addresses on OSes with IPv6 disabled which fails with a protocol not
supported error

This fixes tornadoweb#1809.

tornado/tcpclient.py

@@ -177,7 +177,13 @@ def connect(self, host, port, af=socket.AF_UNSPEC, ssl_options=None,
     def _create_stream(self, max_buffer_size, af, addr):
         # Always connect in plaintext; we'll convert to ssl if necessary
         # after one connection has completed.
-        stream = IOStream(socket.socket(af),
-                          io_loop=self.io_loop,
-                          max_buffer_size=max_buffer_size)
-        return stream.connect(addr)
+        try:
+            stream = IOStream(socket.socket(af),
+                            io_loop=self.io_loop,
+                            max_buffer_size=max_buffer_size)
+        except socket.error as e:
+            fu = Future()
+            fu.set_exception(e)
+            return fu
+        else:
+            return stream.connect(addr)