Refactor method deploy

This change removes the method `_process_items` and refactors the method
`deploy` to do the following tasks:

- `calculate_all_differences_to_deploy`: returns the list of items to be
  created and deleted
- `define_all_tasks`: creates all the task structures
- `upload_all_tasks`: saves all tasks in the common DB

Change-Id: I5cb59dd697875634a4a92df8673c9842a4578d5f
Signed-off-by: gallardo <sgallardor@indra.es>