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.

maxctrl/lib/alter.js

@@ -37,7 +37,13 @@ const maxscale_params = [
     'auth_write_timeout',
     'admin_auth',
     'admin_log_auth_failures',
-    'passive'
+    'passive',
+    'ms_timestamp',
+    'skip_permission_checks',
+    'query_retries',
+    'query_retry_timeout',
+    'retain_last_statements',
+    'dump_last_statements'
 ]
 
 function setFilters(host, argv){