Support stop deployment mechanism

* move cobbler logic for remove nodes action from Naily to Astute;
* api changes: rename node['name'] to node['slave_name'];
* small refactoring;
* add tests.

Implements: blueprint fuel-stop-deployment
Change-Id: Ibc6211d6ec0255178d546fe6ca23b8e2d41e493c
Merge "Support stop deployment mechanism"