TLS fixes:

- don't use password in global context
  - load keys and certs via callback functions
  - don't use gnutls_bye since server is not able to detect dead socket
  - fixed valgrind errors in gnutls

unittest/libmariadb/my_test.h

@@ -555,6 +555,5 @@ void run_tests(struct my_tests_st *test) {
     diag("close default");
     mysql_close(mysql_default);
   }
-  mysql_server_end();
 }