Raise appropriate errors on duplicate Node, Port and Chassis creation

This patch introduces NodeAlreadyExists, ChassisAlreadyExists,
PortAlreadyExists and InstanceAssociated exceptions for
appropriate cases.

Partial-Bug: #1277555

Change-Id: Iec2a7cd09022b6a12afacec9b9b51f8197817ded
Merge "Raise appropriate errors on duplicate Node, Port and Chassis creation"