Revert "engine: Change loading of VdsGroup to load from cache"

This reverts commit 45d7974a1fed8f3cd630b0938eb085d5f3405cf6.

Change-Id: I37fa65971e1b65cd7c8b2100becdc57c3a2a7728
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>