Add API schema for v2.1/v3 remote_consoles 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: Icdb1f87903e3c4345e6533c08b2f2d2f9d36316e
Merge "Add API schema for v2.1/v3 remote_consoles API"