Refactor taskmanager to split heat/native code

Reasons:
 - Trove should be able to manage resource provisioning through:
   - nova, cinder, designate etc. (navites);
   - heat. (orchestration).
 - Main reason is to provide harmless migration from the nova to heat,
   when heat would be cover all required use cases such as
   provisioning/resizing/network-attributes-management.

Changes:
 - Refactoring:
   - dividing actual manager onto navite(nova/cinder/designate/neutron)
      and orchestrator(heat);
   - extracting common code into taskmanager/common.py
   - fixing tests;

Implements: blueprint resource-management-driver