Cloned from launchpad blueprint https://blueprints.launchpad.net/oslo/+spec/oslo-base-manager.

Description:

Managers are responsible for a certain aspect of the system.  It is a logical
grouping of code relating to a portion of the system.  In general other
components should be using the manager to make changes to the components that
it is responsible for.

Manager are used at least in Nova and Cinder, so we should move this code to oslo, and reuse it in both projects.
Also, we are not able to move common Scheduer code (link to bp with scheduler) to oslo without moving manager.

Specification URL (additional information):

None