Rename "manager" to "conductor"

This rename to "conductor" more clearly communicates that this service
has a many-to-many relationship. One or more service instances
coordinate between each other to conduct actions on a set of nodes,
using guarded locks to prevent conflicting simultaneous actions on any
given node. The old name "manager" suggested a more one-to-many relationship,
which is not the design pattern which we use here.

Rename ironic/manager to ironic/conductor
Rename ironic.manager.manager.ManagerService
    to ironic.conductor.manager.ConductorManager
Rename ironic-manager to ironic-conductor
Update docs too

Change-Id: I3191be72a44bdaf14c763ce7519a7ae9066b2bc5