fix have_debug_sync.inc to be more robust

(debug_sync value can have single quotes)

mysql-test/include/have_debug_sync.inc

---require r/have_debug_sync.require
-disable_query_log;
-let $value= query_get_value(SHOW VARIABLES LIKE 'debug_sync', Value, 1);
-eval SELECT ('$value' LIKE 'ON %') AS debug_sync;
-enable_query_log;
+if (`select count(*) = 0 from information_schema.session_variables where variable_name = 'debug_sync' and variable_value like 'on %'`)
+{
+  skip debug_sync is not available;
+}

mysql-test/r/have_debug_sync.require

-debug_sync
-1