core:  storage_domains_with_hosts_view generate slow query

When using the Host tab on the StorageDomain, a very slow query is generated.
The following is a comparison of before/after from a scale environment:

SELECT count(*) FROM vds WHERE ( vds_id IN (select vds_id from 
storage_domains_with_hosts_view WHERE 
storage_domains_with_hosts_view.storage_name 
LIKE 'storage_real'));
 count
-------
    39
(1 row)

Time: 7347.615 ms
SELECT count(*) FROM vds WHERE ( storage_pool_id IN (select storage_pool_id from 
storage_domains WHERE 
storage_domains.storage_name LIKE 'storage_real'));
 count
-------
    39
(1 row)

Time: 528.767 ms

Change-Id: Iab5887ea432de78776340da87ee873733bec7d15
Bug-Url: https://bugzilla.redhat.com/1097160
Signed-off-by: lzelkha@redhat.com <lzelkha@redhat.com>