Handle exception better in v2.1 attach_interface

Add more information when exception occurs in attach interface at Nova
v2.1 API layer.
The commit I7402cfc28d4ee7989c7eb054556df57918bbaeee has been merged
for v2.0 API, this patch does the same change for v2.1 API.

Partially implements blueprint v2-on-v3-api

Change-Id: I1b175501e6db48f27a894db2e66e09d31f8b50e2
Merge "Handle exception better in v2.1 attach_interface"