Add API schema for v3 multinic API

By defining the API schema, it is possible to separate the validation
code from the API method. The API method can be more simple.
In addition, a response of API validation error can be consistency for
the whole Nova API.

Partially implements blueprint nova-api-validation-fw

Change-Id: I62a55c498a1164ff56f82495f720cba67da8483b
Merge "Add API schema for v3 multinic API"