raise better exception for duplicate match

When a duplicate match is found the client previously raised a
NeutronClientException which made it hard for programs using the client
to handle errors. This patch now  makes it raise a
NeutronClientNoUniqueMatch  exception instead.

Fixes bug: 1200323

Change-Id: I6ef6f9a9e257104f676dde7ec26be98417ec70e0
Merge "raise better exception for duplicate match"