Bug 1743: Fixed resolving of Identityrefs in xml.

Fixed resolving of Identityrefs when DataSchemaNode is defined as LeafListSchemaNode.
This is bugfix for: https://bugs.opendaylight.org/show_bug.cgi?id=1743

The overloaded methods toSimpleNodeWithType were refactored with resolveValueFromSchemaType method.
No code duplicity anymore which should prevent similiar bugs in future.

Change-Id: I6d974059369b46470ea81bdfc7694157d09bd2ed
Signed-off-by: Lukas Sedlak <lsedlak@cisco.com>
Merge "Bug 1743: Fixed resolving of Identityrefs in xml."