Add API schema for v3 evacuate 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: I7587fd8c27b820b2a9b751f9c9ae30da0aa41ec7
Merge "Add API schema for v3 evacuate API"