userportal : Fix DiskForVmGuid high CPU

In this patch we remove the need to load all disk data and just load the
required information for the user portal.

Bug URL: https://bugzilla.redhat.com/show_bug.cgi?id=971237

Change-Id: Iceb6e518936f65403561703e6b70920fbcc1f07c
Signed-off-by: lzelkha@redhat.com <liran.zelkha@gmail.com>