core: sync luns info after ConnectStorageServer

* Introducing SyncLunsInfoForIscsiStorageDomainCommand:
  used for synchronizing the DB with the LUNs details
  comprising the storage domain.
* The command is called after ConnectStorageServer
  (which is invoked on activate storage domain).

Change-Id: I5867ad8d36f329e23c611079512be30a9c5f83a5
Signed-off-by: Daniel Erez <derez@redhat.com>