BUG 1162 - problem to post list data

If last path arguments of instance identifier are list with keys then in
POST operation it is necessary to append it to instance identifier as
nodeWithKey.

This code was part of RestconfImpl but it was probably deleted
accidentaly.

Change-Id: I117cbcc39dcb97e8bc5ecc852ce2e9e7da7070cf
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>