core: fixed search Disks when filtered by data-center

Similar to fix in chnage-id I04e37501b29a17a634e31e8875d63577e5f9f401
(and following change-id I862873171c6753f8c8863c10c336e981e39dc8cb),
searching disks (or clusters) by a data-center looks like [1].

I.e. the left outer join is being made on
storage_pool_with_storage_domains; which leads to multiple
records since a data-center can contain multiple storage domains.

Therefore, reverted to previous search so it uses the
'use-tag' syntax [2]. As a result, a similar issue with
search Clusters when filtered by data-center has been
fixed as well.

[1]
SELECT all_disks.* FROM all_disks
LEFT OUTER JOIN storage_pool_with_storage_domain ON
all_disks.storage_pool_id=storage_pool_with_storage_domain.id
WHERE  storage_pool_with_storage_domain.name ILIKE 'dc35'
AND all_disks.disk_storage_type = '0'

[2]
SELECT * FROM all_disks
WHERE (disk_id IN (SELECT all_disks.disk_id FROM all_disks
LEFT OUTER JOIN storage_pool_with_storage_domain ON
all_disks.storage_pool_id=storage_pool_with_storage_domain.id
WHERE (storage_pool_with_storage_domain.name ILIKE 'dc35'
AND all_disks.disk_storage_type = '0')))

Change-Id: I3a792fb63421c7589ed073fb18cfaac46a7dd3a9
Bug-Url: https://bugzilla.redhat.com/1124584
Bug-Url: https://bugzilla.redhat.com/1124593
Signed-off-by: Daniel Erez <derez@redhat.com>