core: Removing template with disks ends with unused data in the db

When removing a template, the records of its disks weren't deleted from
base_disks table because the call to the delete stored procedure was done
with the id of the image rather then the id of the disk - which caused
to unused records to be left in the table and possible errors when
trying to import the template again (not as a clone).

Change-Id: I86573e91885085bcdfc30ee4e966590901a62067
Signed-off-by: Liron Aravot <laravot@redhat.com>