Add API schema for v3 rescue 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 consistent for
the whole Nova API.

Partially implements blueprint nova-api-validation-fw

Change-Id: I3d08bc20e4c585dca1e218e8d97b208d158a3096
Merge "Add API schema for v3 rescue API"