core: Use storage helper to fetch (related to BZ882825)

Added engine support for connecting LUN with multiple connections of different
storage types.

Change-Id: Ida526dd9e08bc9881e65a529cb1b00aee0786af1
Related-to: https://bugzilla.redhat.com/882825
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>