Description of problem:
Right now when creating a large block disk (the larger the disk,the larger the problem)
and marking "wipe after delete" flag as 'True',then removing this disk.
disk existence is wiped from the UI while actually,removing this kind of disk takes a lot of time(since vdsm has to fill the whole disk with zero's).
this can be very misleading to an unaware sysadmin.

for example:
Deleting two 30G disks(wipe_after_delete='True') on iscsi took almost 25 minutes
async task table reported this two assignment as being executed

engine=# SELECT step_id,action_type,task_params_class from async_tasks;
               step_id                | action_type |                     task_params_class                     
--------------------------------------+-------------+-----------------------------------------------------------
 e7c89068-df9d-4ff4-ac63-8d6e6d9bed98 |         230 | org.ovirt.engine.core.common.action.RemoveImageParameters
 c961cc72-ae3d-4d03-9463-6750e28f8228 |         230 | org.ovirt.engine.core.common.action.RemoveImageParameters
(2 rows)

lv's were activated and writable

6c65483f-5316-474a-b04b-4cb397a8a870 db7d2a45-45e7-457c-b40f-47670dda811d -wi-ao----  30.00g                                             
  7c163ea3-fe24-435f-a9e1-dcfe9093d2c0 db7d2a45-45e7-457c-b40f-47670dda811d -wi-ao----  30.00g 

and during all this time (25 minuts),UI reported on an unused ISCSI domain(with no disks or vm's on it) with 1G free space(out of 65G)

RFE is needed to help user follow the process of deleting this kind of disk

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