core: add support for instance type

This patch introduce Instance Types:
Add Instance and Image type id to vm, which links to the instance/image
type it was created from.
Add new Types to VmEntityType enum, and add a field to template which now can be Template/Instance/Image
Type.

Change-Id: I110e74c6fc8906e3d257c7cf31d2af2b1b800218
Signed-off-by: Omer Frenkel <ofrenkel@redhat.com>