core: adding OvfHelper

OvfHelper is a helper class that encapsulates the bll logic that needs
to be done on the ovf read data before using it in the bll project.

Change-Id: I3bfc4094178d90e7b0583db4e427fc2b195a367d
Signed-off-by: Liron Aravot <laravot@redhat.com>