Add comments to select @@version queries to bypass ProxySQL interception

ProxySQL now responds directly to `select @@version` queries, which prevents
these queries from reaching the backend MySQL server. This commit adds
`/* set_testing */` comments to these queries in test files to prevent
perfect match interception and allow them to run on the backend.

Modified files:
- test/tap/tap/utils.cpp
- test/tap/tests/set_testing-240.h
- test/tap/tests/set_testing.h
- test/tap/tests/test_firewall-t.cpp

test/tap/tap/utils.cpp

@@ -400,7 +400,7 @@ int set_admin_global_variable(MYSQL *mysql, const string& var_name, const string
 int get_server_version(MYSQL *mysql, string& version) {
 	char query[128];
 
-	if (mysql_query(mysql, "select @@version")) {
+	if (mysql_query(mysql, "select /* set_testing */ @@version")) {
 		fprintf(stderr, "Error %d, %s\n",
 				mysql_errno(mysql), mysql_error(mysql));
 		return exit_status();

test/tap/tests/set_testing-240.h

@@ -474,7 +474,7 @@ int detect_version(CommandLine& cl, bool& is_mariadb) {
 		return 1;
 	}
 
-	MYSQL_QUERY(mysql, "select @@version");
+	MYSQL_QUERY(mysql, "select /* set_testing */ @@version");
 	MYSQL_RES *result = mysql_store_result(mysql);
 	MYSQL_ROW row;
 	while ((row = mysql_fetch_row(result)))

test/tap/tests/set_testing.h

@@ -473,7 +473,7 @@ int detect_version(CommandLine& cl, bool& is_mariadb, bool& is_cluster) {
 		return 1;
 	}
 
-	MYSQL_QUERY(mysql, "select @@version");
+	MYSQL_QUERY(mysql, "select /* set_testing */ @@version");
 	MYSQL_RES *result = mysql_store_result(mysql);
 	MYSQL_ROW row;
 	while ((row = mysql_fetch_row(result)))

test/tap/tests/test_firewall-t.cpp

@@ -58,7 +58,7 @@ int main(int argc, char** argv) {
 	MYSQL_QUERY(mysqladmin, "load mysql variables to runtime");
 	
 	// Test that firewall initialized and blocks all queries
-	if (mysql_query(mysql, "select @@version")) {
+	if (mysql_query(mysql, "select /* set_testing */ @@version")) {
 		int myerrno = mysql_errno(mysql);
 		ok(myerrno == 1148, "Any query should be blocked");
 	}