Initial part of conductor implementation

* only local mode is now supported;
* conductor api defined;
* db backend implementation started;
* cluster ops sample added.

TODO:

* move model_base to the new place;
* move models to the new place;
* move all existed db methods from storage.py to the new place;
* check that it works correctly;
* write simple unit tests for it;
* ?

Partially implements blueprint ng-arch-conductor

Change-Id: Ib4cb308a6cac9efca476b27d003d375458dce682
Merge "Initial part of conductor implementation"