Config params substitution handled in managers

Loading from external configs is required for auto deployment
fuel-stats packages by the DevOps team.

For collector COLLECTOR_SETTINGS environment param is used.
Value of COLLECTOR_SETTINGS should be path to external config.
Config is regular python file. For collector standard Flask
external config file feature is used.

From collector config removed unused HOST and PORT params

For migrator parameter '--config' is added to manage_migration.py.
External config is yaml config file.

Blueprint: send-anon-usage
Change-Id: I3667d22d55b6edbbaa8f81e14dcd3d199e7a87a6