Update the test framework so that the need for test_main is removed.  Everything
that needed test_main now works using the same infrastructure as tests that used
register_tests.

This meant:
* renaming register_tests to setup_tests and giving it a success/failure return.
* renaming the init_test function to setup_test_framework.
* renaming the finish_test function to pulldown_test_framework.
* adding a user provided global_init function that runs before the test frame
    work is initialised.  It returns a failure indication that stops the stest.
* adding helper functions that permit tests to access their command line args.
* spliting the BIO initialisation and finalisation out from the test setup and
    teardown.
* hiding some of the now test internal functions.
* fix the comments in testutil.h

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3953)
diff --git a/test/tls13secretstest.c b/test/tls13secretstest.c
index e052d0b..9f32fdf 100644
--- a/test/tls13secretstest.c
+++ b/test/tls13secretstest.c
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 2016-2017 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -384,7 +384,8 @@
     return ret;
 }
 
-void register_tests()
+int setup_tests()
 {
     ADD_TEST(test_handshake_secrets);
+    return 1;
 }