core: add StorageDomainOvfInfo entity/db

This patch adds the StorageDomainOvfInfo entity along implementation of
the needed dao and stored procedures.
This entity is used to determine which disk is used as the ovf store of
each domain and if the ovf data on that disk is up to date.

Change-Id: I6cd52f5b9f14559bcec224dee868cf267cd15ebe
Signed-off-by: Liron Aravot <laravot@redhat.com>