Add API schema for v2.1 access_ips extension

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 consistent for
the whole Nova API.

Partially implements blueprint v3-api-schema

Change-Id: I495e7538e5d8d67f19792dfa0427ab7a1b0068cf
Merge "Add API schema for v2.1 access_ips extension"