Allow to set workers for neutron

This change adds ability to set custom workers number for neutron
(rpc and metdata workers), in the same time if workers parameters aren't
defined in pillar, backward compatibility is kept and hardcoded values
from template will be used.

Change-Id: I4bc91b669a465b73ef610b53fbe960cae3911bdb
Related-Prod: https://mirantis.jira.com/browse/PROD-16465
30 files changed