Bug 1355: Fixed incorrect input keyword use in rpc

Fixed incorrect evaluation in method flattenInput in NetconfMessageTransformUtil.
Added test for testing toRpcRequest and flattenInput methods.
Added test model for test.

Change-Id: Id6938b39f0bd06b315f4820a6c1008fa371416d0
Signed-off-by: Lukas Sedlak <lsedlak@cisco.com>
Merge "Bug 1355: Fixed incorrect input keyword use in rpc"