Multiple PNFs with same ModelInfo but different instance name not able to be instantiated

When instantiating a service with multiple PNFs, SO differentiates them using ModelCustomizationId. This causes issues when creating multiple instances of same model resource, and each lookup would return the same object.
With this patch, Instead of using ModelCustomizationId, we enable SO to use instanceName parameter to differentiate the PNFs.

Issue-ID: SO-3948

Signed-off-by: Aleem Raja <aleem.raja@t-systems.com>
Change-Id: I9dd039ac786a60f7cf4d4a9c456c7681f64d6786