Interrogation ROBOT test cases improvements.

Add to ONAP integration e2e for pnp pnf registrate use case test cases enhancements delivered in Guilin release:

• check if "model-invariant-id", "model-version-id" is present in pnf resource.
• check if "model-invariant-id", "model-version-id" is present in service instance.
• check if pnf resource can be reassigned to new service instance when pnf hasn't been deleted during old service instance deletion