core: Added user queries to retrieve instance types and images

Previously the only way to retrieve the instance types/images was
using the search query. Since they will have to be visible also
from user portal, added the specific user queries.

Change-Id: Idfddb6e292010c33fadcaf89bce2a5fb51ff87a8
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>