Better use BIO_snprintf() than snprintf(), in case the later isn't available

Reviewed-by: Tim Hudson <tjh@openssl.org>

test/ssl_test.c

@@ -186,7 +186,7 @@ static void tear_down(SSL_TEST_FIXTURE fixture)
 static int test_handshake(int idx)
 {
     SETUP_SSL_TEST_FIXTURE();
-    snprintf(fixture.test_app, sizeof(fixture.test_app),
+    BIO_snprintf(fixture.test_app, sizeof(fixture.test_app),
                  "test-%d", idx);
     EXECUTE_SSL_TEST();
 }