BUG-1473: update model.util.InstanceIdentifier users

Companion patch to https://git.opendaylight.org/gerrit/9622, updates
users to use the new name. Also make the code a tiny bit more readable.

Fixed conversion to checked Future.

Change-Id: If8da3639e656214713d3680951cd9ae724c5ad6f
Signed-off-by: Robert Varga <rovarga@cisco.com>