bpo-17085: test_socket: cancel scheduled alarm on test failure (#3505)

(cherry picked from commit 71fe8c00f6e2eda39d90c225c5f7635268cc4653)
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index 2b20a79..bef1872 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -733,6 +733,7 @@
                 self.assertRaises(socket.timeout, c.sendall,
                                   b"x" * test_support.SOCK_MAX_SIZE)
         finally:
+            signal.alarm(0)
             signal.signal(signal.SIGALRM, old_alarm)
             c.close()
             s.close()