tools: StorageDomainOvfStoreCount config value

adding StorageDomainOvfStoreCount to engine-config.

Change-Id: If35b26983a2d42d1b950572bdad4e0fbf657c7cd
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1134242
Signed-off-by: Liron Aravot <laravot@redhat.com>