Split ManagerDefault into manager and engine

This patch defines an interface for a new component: policy engine.
The APIs found under this interface are the one we may want to customize
and to configure easily.
This patch also split the current manager code into manager and engine to
provide a default version of the policy engine.

Change-Id: I97cf59760b53d248fe9efe466ae5e73bd7e5cc06
Signed-off-by: François Gaffie <francois.gaffie@intel.com>