Add API schema for v2.1/v3 reset_server_state 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 v3-api-schema

Change-Id: Ib6bf4d1f1d875249d1758d4414377d47e15a3198
Merge "Add API schema for v2.1/v3 reset_server_state API"