Refactoring maas functions to use config

Use config instead of args.
Adding
* process_fabrics
* process_subnets
* process_devices
* process_machines
* process_dhcp_snippets
* process_boot_resources
* process_package_repositories
diff --git a/_modules/apiclient/maas_client.py b/_modules/apiclient/maas_client.py
index 9a184c5..530e6b2 100644
--- a/_modules/apiclient/maas_client.py
+++ b/_modules/apiclient/maas_client.py
@@ -225,7 +225,8 @@
             POST it as application/json
         :return: The result of the dispatch_query call on the dispatcher.
         """
-        kwargs['op'] = op
+        if op is not None:
+            kwargs['op'] = op
         url, headers, body = self._formulate_change(
             path, kwargs, as_json=as_json)
         return self.dispatcher.dispatch_query(