Follow up of fix for CONC-680:

mysql_old_password is disabled by default (setting DISABLED YES),
but can be used if the plugin was added to the list of restricted
authentication plugins (via mysql_optionsv using option
MARIADB_OPT_RESTRICTED_AUTH).

unittest/libmariadb/my_test.h

@@ -688,6 +688,7 @@ void run_tests(struct my_tests_st *test) {
 
   if (!mysql_real_connect(mysql, hostname, username, password, schema, port, socketname, 0))
   {
+    diag("Error: %s", mysql_error(mysql));
     BAIL_OUT("Can't establish TLS connection to server.");
   }