core: Fix quota count for Template with multiple SD

When deleting a template which have a multiple domain disk, the disk
size was only released from the quota once.

RemoveVmTemplateCommand was changed to support multiple storage domain
disks when removing templates.

Change-Id: Id2f5051218405753dc86b997aaa47f488f159350
Bug-Url: https://bugzilla.redhat.com/963587
Signed-off-by: Ofri Masad <omasad@redhat.com>