MXS-2200: Add runtime handling for all global parameters

All global parameters are now handled by the runtime configuration
modification code. The parameters that are trivial to update can now be
updated at runtime. All other global parameters cause a new error message
to be returned stating that the parameter in question cannot be modified
at runtime.

Also updated the list of modifiable parameters in MaxCtrl. This list
should not be stored in MaxCtrl and should be created by MaxScale at
runtime.

server/core/config.cc

@@ -2632,6 +2632,38 @@ static int handle_global_item(const char* name, const char* value)
     return processed ? 1 : 0;
 }
 
+bool config_can_modify_at_runtime(const char* name)
+{
+    for (int i = 0; config_pre_parse_global_params[i]; ++i)
+    {
+        if (strcmp(name, config_pre_parse_global_params[i]) == 0)
+        {
+            return true;
+        }
+    }
+    std::unordered_set<std::string> static_params
+    {
+        CN_USERS_REFRESH_TIME,
+        CN_LOCAL_ADDRESS,
+        CN_ADMIN_ENABLED,
+        CN_ADMIN_SSL_CA_CERT,
+        CN_ADMIN_SSL_CERT,
+        CN_ADMIN_SSL_KEY,
+        CN_ADMIN_HOST,
+        CN_ADMIN_PORT,
+        CN_LOG_THROTTLING,
+        "sql_mode",
+        CN_QUERY_CLASSIFIER_ARGS,
+        CN_QUERY_CLASSIFIER,
+        CN_POLL_SLEEP,
+        CN_NON_BLOCKING_POLLS,
+        CN_THREAD_STACK_SIZE,
+        CN_THREADS
+    };
+
+    return static_params.count(name);
+}
+
 /**
  * Free an SSL structure
  *